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Disambiguous.png This article is about the mission in Mass Effect 2. For the mission in Mass Effect 3, see Priority: Horizon.
Another typical Terminus colony without colonists

The Illusive Man has received information about a potential Collector attack against the small colony world of Horizon.


After acquiring Archangel, Jack, and Mordin Solus, as well as recovering the tank from Korlus (note that waking up Grunt is not necessary), Shepard will be unable to select a new destination for the ship. If you attempt to access the Galaxy Map, both Kelly Chambers and Joker will inform Shepard that the Illusive Man wants a chat. Shepard must go to the FTL comm room to talk to him and begin this mission.

If the player has the requisite Downloadable Content (or is playing Mass Effect Legendary Edition which includes almost all such DLC by default), it is possible to acquire both Zaeed and Kasumi before acquiring the four teammates mentioned above; this allows Shepard to have as many as eight team members (including Jacob and Miranda) before the mission on Horizon begins.

Note: By delaying recruitment of one of the four original squad members, Shepard can take time to reach a higher level by completing all available N7 assignments, along with assignments on the Normandy, Omega, and Citadel. Also, if the corresponding DLCs are present, Normandy Crash Site, Zaeed's and Kasumi's loyalty missions, Overlord and Firewalker Pack can be completed as well. Delaying Horizon in this way is also one of the two ways Shepard can be maximized in level before encountering the Collector Ship mission.

This mission is the actual field mission acquired after arriving on Horizon following Stop the Collectors: Go to Horizon. It begins once Shepard arrives on the planet.


Most enemies will have biotic barriers, and some will have armor as well. An ammo power such as Warp Ammo, which provides bonuses against both barriers and armor, helps quite a bit as well, but if Shepard is only trained for pistols and SMGs, you may want to bring at least one squadmate who can use a bigger weapon. There are several points where you face waves of Husks - remember that abilities with a force component such as Flashbang Grenade, Concussive Shot or Pull will instantly kill any Husk that is not protected by armor.

One of most useful squadmates in terms of what she brings to the table is Kasumi, if you have completed her Loyalty mission. Her Loyalty power, Flashbang Grenade, aside from having great crowd control utility against even enemies with full barriers, can disable the biotic attacks of certain dangerous foes (which will come in handy later in this mission). Additionally, her Shadow Strike power does huge damage and can be used to methodically pick off enemy troops.

Meanwhile Grunt is also excellent for this mission due to his sheer durability, his Incendiary Ammo, and his effectiveness against husks. Consider bringing Miranda for her Warp power, especially if Shepard doesn't have it; the extra health she provides to the squad also certainly won't hurt.

For heavy weapons, you can choose between the Cain for use in the final battle, or a weapon with a large area of effect good against multiple charging foes such as the M-622 Avalanche or the Arc Projector.


Mission Briefing[]


The Illusive Man will give Shepard information about the mission. Shepard agrees to go to the colony in order to save it. After talking with the Illusive Man, Shepard walks to Mordin’s Tech Lab to ask him if he has developed a countermeasure to the seeker swarms. He will reply yes and show Shepard the schematics.

Horizon Before Normandy’s Arrival[]

Horizon had been recently fitted with GARDIAN laser turrets which were provided by the Alliance to defend the colony. The turrets, however, could not be calibrated correctly, and so the Alliance had sent either Ashley Williams or Kaidan Alenko to help get the turrets functioning, depending on the Virmire decision in Mass Effect.

The Collectors attack Horizon after establishing a communications blackout. While Shepard's former squadmate is talking with one of the colonists, Lilith, the Collector Cruiser drops into the atmosphere and the seeker swarms are released. The former squadmate will try to provide cover but ends up getting stung and incapacitated. The colonists run for cover as the swarms sting more and more people.

Arrival On Horizon[]

A Collector on Horizon

Landing on Horizon, you find the Collectors in mid-operation: they have started moving colonists into their ship. Your job this time is to hit them and stop them before they get away. As you move away from the landing site, Mordin will tell you that his countermeasure for the swarms may not work because they haven’t had a decent test yet. With that somewhat questionable reassurance, move forward and prepare to engage the enemy.

Combat Strategy: Move carefully between cover locations for good angles and take out the attacking Collectors one by one. Don’t move forward too quickly, as some reinforcements will fly in to replace the fallen. Even though all Collector soldiers look very similar you will be engaging several distinct types: the basic Collector Drones, and the much tougher and more damaging Collector Guardians and Collector Assassins. Assassins unleash deadly particle beams, while the Guardians fire powerful rifles at you from behind their pop-up circular shields that may remind you of the hexagonal barriers used by the geth in the first Mass Effect game. For some useful tips on dealing with these foes, see their own pages.

Once all the Collectors are down pick up the heavy weapon ammo in the middle of the area where the Collectors were; a little way ahead, hack the datapad on the picnic table for 6000 credits and then move on. The next area that you come across will have several buildings around, and Collectors who just happened to be harvesting. Move into cover and take them out quickly. You'll also encounter something else that you may recognize from the first Mass Effect: husks. This time they only have melee attacks, so them out from a distance; biotics are effective as is shooting their lower halves. A good way to end this fight quickly is to use the buildings on either side to flank the Collectors with your squadmates or yourself. Once the enemies fall, go into the building on right for a datapad worth 4200 credits. Outside the building is a dead Collector, which you can scan for a Heavy Skin Weave upgrade.

A fallen husk found on Horizon

Around the corner is a dead husk. A cutscene will play and Shepard will describe how they are different from the ones encountered on Eden Prime, or Mass Effect in general. Shepard and the squad realize that the Collectors must have come with these husks and not created them on-site. As time is of the essence, Shepard orders the squad to press on in hopes of preventing any more abductions.

Enter the next area slowly and put your squad in cover if you wish. Before you do so run up the stairs from where you enter to bypass a wall safe for 4800 credits and Medi-gel in the building to the left. Once that is done, move into cover and take out the attacking Collectors. Use cover and the buildings to flank the enemy to make things go a little bit faster.

"Assuming Control Of This Form"

Once the battle is over, do not go past the pods further up or where the path narrows as more Collectors will spawn. Instead, move around this area collecting items and equipment. You will find a med kit in a building to the left of where you entered. Move across from that building to where you see some colonists in stasis on some stairs. Continue up those stairs to find ammunition and a computer in the room at the top for 3000 credits. Going down, look in the center of where you just fought to pick up the Collector Particle Beam heavy weapon. Picking up the Particle Beam will also totally refill your heavy weapon ammo if you are not at full capacity so you may want to use that strategically. If you miss or ignore it here, it may also be found in two other instances on this mission (see its page) or it will be awarded automatically at its conclusion. Once you are ready, save your game and move into the next area.

Once you pass a certain point, a brief cutscene plays showing more Collector troopers arriving as airborne infantry. Here, Shepard will encounter Harbinger for the first time. He will assume control of other Collectors and direct the battle, often taunting Shepard. He is a formidable foe, possessing barriers, armor (but no health), and powerful biotic attacks. Any time Harbinger possesses a Collector, take him down first, then quickly target the others so he can’t do it again. He can only possess one Collector at a time, but will frequently possess a Collector that is almost dead and make it beyond full strength again. Move around this area for cover and use it to eliminate your foes. Once they are down move around and recover the power cells in a building to the west and a computer containing 3000 credits immediately to the north of the Particle Beam's location. Move to the large doors to the south and bypass them to enter the structure.

Insanity Tips:

  • It is possible to retreat back from the area where the Collectors appear and head up one of the staircases on the right for a safer vantage point. Alternately, you can take cover with your squad in the building on the left. Going through the door of this building a short ways triggers the fight, but you can retreat back inside and even close the door to be extra safe once it begins. You can then pop out of the door to deal damage and then retreat back inside the building as many times as needed to finish the fight.
  • A useful tactic in fights with Harbinger is to strip away all of his weaker allies before taking him on. As long as you do not let him get too close or take too much damage from his attacks, this will prevent you from facing multiple Harbingers in a single battle. If you at least remove the weaker Drones he will be forced to possess one of his more valuable Guardians or Assassins. This tactic can be made even safer if you distract Harbinger with a Combat Drone or disable its attacks with Flashbang Grenade while focusing on its lesser minions.
  • Harbinger will perfectly lead you with his fast moving Warp-style attack if you are moving in one direction but changing direction when he fires or slightly after can make it miss. At short range the bolt is fast moving enough that it's more difficult to dodge.
  • Harbinger's slow moving Singularity-style seeking attack knocks Shepard out of cover accompanied by a temporary stun which can leave you fatally vulnerable to incoming fire. When you see it coming, move back and forth behind your cover or temporarily displace to lead it away. Like Singularity, this ability lingers for a time when it impacts a piece of cover, effectively denying it from being used as cover for the duration.


Delan the mechanic

Once you move inside far enough you encounter an unharmed colonist, the local mechanic, Delan. You can get some information about the attack, where your former squadmate is, what towers were installed and his anger at the Alliance, and you can earn some morality points as well. You determine from the conversation that the GARDIAN laser towers are the key to destroying the collector ship. Once you are done talking he will tell you to move to the spaceport to get the towers operational.

Once you finish your conversation, use the weapons locker in the garage if you want (remember that if you picked up the Collector Particle Beam earlier that is now your Heavy Weapon so change it now if you want something different), but don’t forget to pick up the platinum, medi-gel and access the wall safe to get 6000 credits. Move towards the door and beyond. Save your game before leaving.

Get to the Starport[]

Good cover places: the obstacles southeast and the stairs (just watch for flankers from the back)

The next area is difficult because of the lack of cover and the enemies' spawn points. As you near the edge of the wall to the right, move into cover and position your squadmates where you can cover them or vice versa and take out the attacking Collectors, husks, and Scion. A Scion has a powerful attack similar to Shockwave, and Harbinger also makes an appearance every now and then. If you remain behind the low thick wall that first separates you from the area with the Collectors, Harbinger's slow singularity-type attack will not be as effective at knocking you out of cover, and you will have a good vantage point to take him out along with ihis smaller minions. If Harbinger or the Scion is about to come around the wall, run back to the large piece of farm equipment and circle around it as necessary.

Insanity Tips: If you have Kasumi in your party, her Flashbang Grenade can be used to temporarily prevent Harbinger from using biotic abilities, giving you plenty of space to kill him; this works even if Harbinger's barriers are full, and lasts considerably longer than the power's duration and even cooldown time, meaning that through repeated uses you can completely suppress Harbinger's warp and singularity attacks, leaving him only with his gun (which is never fired). Conversely, against the Scion the power only suppresses its attacks for the brief stated duration of the power—however Kasumi's Shadow Strike power can momentarily distract it. On Insanity it is usually best to save the Scion for last because of its toughness and slow movement rate. It can be tough to keep your squadmates alive against it but they will revive after you've cleared the area and the Scion is the last major hurdle so consider saving your medi-gel if they do go down.

Once the enemies have fallen, move around and collect the clips that they dropped. The area also contains some power cells on a walkway to the left of the entrance and a computer with 3000 credits on the upper level. To the right is a dead Collector that yields a Hyper-Amp research upgrade. Once you have these items, move to the doors of the Starport, save the game, then bypass the doors and enter the Starport.


Many ways to deal with these guys (HINT: melee isn't one of them)

Move to cover and be prepared for a husk mass attack and two Scions. You enter at the west end of the Starport, where the back of a truck offers a possible cover location. On the south side there is less cover, though Power Cells are to be found up some stairs. On the north side is a balcony that provides some cover and long lines of fire, along with the Starport's single Medical Kit. Finally, at the far east end there are some L-shaped cover locations that you may soon find useful for evading Husks, since when playing higher difficulty levels they are the greatest threat due to their numbers and melee combat style. If you have trouble with this fight, several proven battle plans are available:

Plan A - Hiding in the Truck: One way to deal the husks is to climb on the vehicle to the left of entrance. While the husks can follow you, with a powerful enough melee punch, you can knock them back to the ground. In addition, this vehicle contains a respawning clip. On top of that, the platform's location could confuse the Scions that appear until you can deal with Husks. Choosing this vehicle also means there is only one direction the Husks can attack you from—so there will be a lot of enemies in one tight space, ready to be taken out with area-of-effect powers. The principal risk of this strategy involves getting trapped in the truck with too many Husks blocking any possible escape route.

Plan B - Confuse the Husks: On Insanity it may be best to avoid getting cornered in the truck, and instead mount a "mobile defense" running away from husks while keeping obstacles between you and the Scions. Note that vaulting over obstacles, especially the large L-shaped covers at the far east end of the field, will force Husks to take a long circuitous route to get to you. If you end up with them coming at you from several directions at once that's usually the best solution. The very first Husk will appear, alone, on your left: if you kill it quickly and proceed clockwise around that north side, you will have more cover from the Scions than the south side offers. Once you reach the far east end, you can use the L-shaped covers to confuse the Husks for long enough to pick them off with powers and weapons before the Scions get too close.

Plan C - Nuke the Scions: Bring the M-920 Cain to take the Scions out of the picture quickly. Simply move into the area to trigger the fight as normal and begin charging the Cain while aiming for a spot on the top of the raised platform where the transmitter is located. The resulting explosion should kill or nearly kill both Scions; finish them off and then deal with the husks which shouldn't be too hard with the threat of the Scions lifted.

Plan D - Exploit the Glitch: You can make the fight partially easier before it starts by moving to the far right or far left side of the doorway, where you should just be able to see part of one Scion. You can now take it out without it being alerted to you. A sniper rifle is highly recommended for this as it will allow squadmate powers—as well as your own—to be aimed more effectively. A heavy pistol, Warp or Incinerate will also be effective. After one Scion is dead, stand to the other side of the staircase to defeat the second Scion. If both Scions are defeated without detection, no Husks will spawn. If you are quick enough with hacking, you will be able to skip the whole first fight with Scions and husks.

This is most of the good cover positions in the starport - position yourself and your squadmates wisely

Once the enemies have fallen and before you go to the transmitter, there is a crate of heavy weapon ammo to the far right of where you came in through the doors; opposite this on the raised deck to the far left of the doors where some of the husks attacked from is a med kit. You can save either of these for later but be warned it may be more difficult to get to them as you will be in near constant combat for the rest of the mission.

Once you are ready, hack the transmitter. Shepard will ask EDI to realign the lasers and bring them online. However, there is a hitch: the lasers will take time to charge, so you have to defend the tower. Prepare for a hard fight.

Defend the Tower[]

This fight is challenging because enemies will attack in multiple waves from multiple locations. There are a total of three waves that you will have to fight off:

  1. The first wave consists of two Husks, a Collector Assassin, a Guardian, several Drones, and Harbinger. They will initially spawn toward the southeast end, between the power cells and the L-shaped covers.
  2. The second wave will contain a Guardian, two more Drones, and tends to spawn at the northeast end, between the balcony with the medical kit and the L-shaped covers. Harbinger will quickly take control of one of the drones; he will be mobile and move around to try and flank you, while the Drone and Guardian take cover.
  3. The third wave initially starts with four Husks, an Assassin, a Drone, and Harbinger. The Collectors spawn to the northwest of the area, between where you initially entered and the balcony with the medical kit. The husks will spawn from the raised balcony with the medical kit on the north, so don't be there. As you kill the Collectors they are replaced close to their original position. Between two to four replacements are made after any of the Collectors are killed.
When the going gets tough use your heavy stuff - ammo crate pictured

Combat Tips:

  • The most important tip about where to fight in this section is: as far as possible from where the Collectors arrive, because that gives you time to pick off any Husks before the attacks of the Collectors become too overpowering. For the first two waves, you can hold a position near the north or west side--for instance the balcony on the north with the medical kit, which gives you good lines of fire.
  • After the second wave one of your squadmates will make a comment. That means it's time to move. A great place to get ready for the last wave is at the far east end among the L-shaped covers. The Husks will reach you long before the Collectors.
  • Deal with Husks quickly in each wave, because if they reach point blank range they can knock you out of cover exposing you to deadly fire from the Collectors.
  • If you are crouching behind low cover, remember that Harbinger's slow singularity attack can dislodge you, so slide back and forth to keep it from finding you.
  • Avoid wasting time and ammo shooting out the umbrella shields of the Collector Guardians and instead try to flank them or wait for an opening.
  • Between each wave you'll have at least a little time to move around, grabbing ammo and changing position if desired.
  • Stay in cover, put your squadmates in cover and focus on keeping the enemy off your flanks.
  • On Insanity difficulty your squadmates, even the mighty Grunt, have a very tough time surviving while trading shots against the Collectors especially once Harbinger joins in. If you don't want to be constantly reviving them with medi-gel, keep them near you and therefore hopefully far away from the Collectors. If they're especially frail, you can put them completely out of the line of fire and only use them for their powers while you do the heavy lifting.

EDI will keep you up to date on the status of the lasers, and once they reach 100 percent, you know the fight is almost over. However, there is one more problem.

The Praetorian[]

A praetorian emerges from the Collector cruiser

Once the Collectors get whittled down and the lasers are near full charge, Harbinger sends in a Praetorian. A Praetorian is a deadly enemy, but it is the only opponent you have to deal with for this fight. The Praetorian has two deadly attacks, Death Choir and the particle beams it shoots from its eyes. The Praetorian itself has just two levels of defense: barriers and armor. When its barriers drop, you'll want to put as much damage on it as possible quickly, because it will soon glow and slam to the ground: this is its "Death Choir" ability that will stun and then instantly kill you if you are too close. The shockwave from this attack penetrates cover as well; the only way to be safe from it is to be far enough away not to be hit when it lands. When the Praetorian is on the ground and glowing immediately following a Death Choir, it is temporarily invulnerable so don't shoot at it because you will waste your ammo. Typically one of your squadmates will probably shout something about their attack being ineffective, and if the Praetorian is currently not in your line of sight, that will be your cue to take special precautions. This is a good time to revive squadmates, search for a thermal clip, or recharge your shields and health. Once it takes off again, open up. Repeat this process until the Praetorian disintegrates in midair.

Combat Strategy: The basic strategy for this fight (and any fight against a Praetorian) is to play "Ring Around the Rosie" with it: find a piece of the environment with decent cover that you can lead it around in circles while your squadmates and you chip away at it carefully bit by bit. This is about patience and care, not brute force; keep your distance and interpose cover between yourself and the particle beams when they are firing. The Praetorian only chases and targets Shepard, so as long as your squadmates are in cover far enough away not to get hit by a Death Choir they won't go down. Just keep circling and your squad will eventually kill it in a war of attrition, though of course you should contribute damage as long as you can do so without taking too much damage or getting too close. If the Praetorian activates its Death Choir (which happens after you inflict a lot of damage to its armor or you get too close), back up quickly to make sure you're outside the blast radius, then resume hitting it with guns and powers once it resumes its attack. Powers such as Warp or Incinerate that can arc around cover definitely come in handy here as you can hit the Praetorian without exposing yourself to return fire, but even without this it will eventually go down from your squad's fire. If ammo is a concern save it for damaging the Praetorian's armor and not its barrier which regenerates after every Death Choir attack.

Legendary Edition: If you brought Kasumi on this mission for her Flashbang Grenade, combining Flashbang Grenade with an engineer's Combat Drone substantially slows the rate the Praetorian chases you around the map.

After the Fight[]

The Collector cruiser bugs out

The activated GARDIAN towers hammer away at the Collector cruiser, forcing it to retreat with about one-third of Horizon's populace. After the battle is over, Shepard meets with the former squadmate. If Ashley or Kaidan had been a romantic partner in Mass Effect, a brief cutscene plays showing their reunion. The mood quickly changes when the former squadmate discovers that Shepard is working with Cerberus. Ashley or Kaidan reveals that he or she had been dispatched to Horizon after the Alliance received a tip that Horizon was the next colony to get hit. They also came to the colony in part to learn whether Cerberus was behind the attacks on the colonies. The former squadmate is highly upset about Shepard's alliance with Cerberus. Ashley or Kaidan questions Shepard's loyalty and refuses to join Shepard's mission. From the conversation, you learn about what has happened over the last two years and what Shepard missed while being on an operating table.

Once you are done, you automatically return to the Normandy.


You are immediately taken to a holo-conference with the Illusive Man. He is impressed that Shepard's squad managed to stop the Collectors from destroying the colony. However, Shepard is not pleased to discover that the Illusive Man had leaked information on Shepard's relationship with Cerberus; the Illusive Man admits he lured the Collectors to the colony because he was not willing to wait for them to strike. He also questions whether you have put your past relationship with Ashley or Kaidan behind you; answer honestly, bluff him, or rebuff him as you choose.

Through their attacks on the SSV Normandy and human colonies—notably a colony where one of Shepard's former squadmates was located—the Collectors have made clear that they are after humans in general and Shepard in particular. The Illusive Man says he will devote all of his efforts to finding a way through the Omega 4 Relay and adds that Shepard should keep building the team. To this end, he hands over three more dossiers of new potential recruits.

If you established a romantic relationship with the Virmire survivor in the first game, you'll receive an email from them once they've calmed down from seeing you with Cerberus (see their character pages for transcripts). Even if you weren't romantically involved, Kelly Chambers will question you about your relationship with them whenever you speak to her, with more pointed questions about any romantic interest if they are the opposite sex of Shepard. You can also have a brief conversation with Joker about your mutual former crewmate in the cockpit.

E-Mail Message (Can you help?)[]

Upon completion of the mission, you'll also receive this letter from a colonist. The Alliance soldier mentioned in the letter can either be Kaidan or Ashley.

From: Robyn Reeve


The Alliance soldier here gave me this contact information -- I hope this reaches you.

You said you were trying to stop those Collectors. They took my son and my brother. Have you found them? Do you know where they are? I know you're looking, but so many people are just gone. Every family lost someone. The children are the worst. Empty desks at the schools, winter clothes that never got worn.

Please. The Alliance isn't doing anything. The Council isn't doing anything. If you can find our people, I'm begging you to do something. Tell me something I can do.

Tell me anything.

Robyn Reeve


Mission Summary[]

Collectors escaped with approximately one third of Horizon's population. Front corporation will funnel supplies, monetary aid to colonial survivors. Collector leader, Harbinger, demonstrates a personal interest in Shepard. Unclear whether his ability to possess his minions is cybernetic override, indication of hive mind among Collectors, or even Reaper technology at work. Salvage teams captured Collector bodies for study.