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Disambiguous This article is about the mission in Mass Effect 3. For the mission in Mass Effect 2, see Horizon (mission).
What price will you put on your family's safety? Come to Sanctuary.

Cerberus may be using the Sanctuary facility on Horizon as a cover for secret activity. Land on Horizon to search for clues about their operations.


Prerequisite: Priority: Thessia

Samantha Traynor tracks Kai Leng to Horizon after the failure of your mission on Thessia.


You will be facing a wide variety of enemies on this mission, but the toughest battles involve large elite Reaper forces. Pick squadmates able to deal with heavy armor and barriers; the ability to create fire or biotic Power Combos is a nice bonus. Equipping your weapons with armor piercing mods will come in particularly handy on multiple occasions.

Note: If Miranda Lawson survived the Suicide Mission, she will be pursuing her sister Oriana, who has disappeared inexplicably. Miranda suspects the hand of their father, Henry Lawson. Eventually, she tracks Oriana to Sanctuary. If Miranda is not alive, you will receive an e-mail from Oriana herself after the events on Thessia, in which Oriana claims to be in trouble at Sanctuary.

Miranda will also e-mail you for up to three times over the course of the game, and action or inaction on these will directly influence the final confrontation:


"Safe and secure" refuge turns out to be a warzone same as the rest of the galaxy

When you are dropped off you see the entrance area to the facility has been nearly destroyed. Your squadmates make a note on it. Walk towards it and a Cerberus shuttle will crash above the entrance, checked upon by a Harvester that apparently shot it down. You can't fight it; it flies off after seeing the wreckage. Shepard remarks that it's about time Cerberus and the Reapers started fighting each other.

A few steps onward and you'll have to deal with two Phantoms that come from the crashed shuttle as well as a Nemesis. The Nemesis takes cover on the balcony barricades while the Phantoms drop down to engage in close range. There's plenty of debris in the area for cover, so take your time dealing with the ladies. When that's done, by the foot of the stairs at the north end of the secluded depression on your right are parts you can salvage for 1,500 credits.

Where the hell is everyone? I want to speak to the manager

Continue into the facility; there is a medical station by the door. The door also seals shut once you enter; there's no backing out. If you paid attention to the eye on the bottom of your screen and pressed the button for navigational assistance, one of your squadmates will point out the Cerberus shuttles seemingly appearing from the tower above and Shepard will say that's where the team is going. But first, if you're not in a hurry, explore the reception area.

Near the windows on the leftmost side, below the conspicuous overhead screens you can examine a terminal with security footage of Sanctuary. In the area apparently used as office space, there are 3 audio logs and a PDA to examine, all pertaining to Sanctuary's refugee processing administration, as well as an inventory log worth 1,500 credits. Clean them out if you want then proceed downstairs.

Sanctuary Reception[]

"All security procedures are in place to protect you and your loved ones

To the left and down the stairs by the crashed Alliance shuttles are 2 audio logs, left behind by civilians by the sound of them. In the lobby to the right as you came down the stairs, the one with the big glowing SANCTUARY logo on it, there a few dead rachni and Cerberus goons. This should alert you to prepare for war, since just beyond the big wall obstructing the view there are 4 live Cerberus Troopers; 2 near the console and 2 next to a dead Ravager.

There's a Pistol Scope mod next to a dead Cerberus soldier in front of the raised desk. Continue through the door labeled POOL MAINTENANCE right next to the SANCTUARY logo. A console will have a recording of Miranda (if she's alive) or Oriana (if she isn't), telling you to turn back and that the facility isn't what you think it is. Watching it is optional, as are most of the succeeding console videos left by the Lawson daughter that you will encounter as you explore Sanctuary.

The room has a wall safe containing unspecified "equipment" by the opening you just came through. Salvage it for 1,500 credits and continue through the large opening that is now to your left.

Indoctrinating the water supply seems smart until it becomes sapient and starts killing all of Cerberus' guys

You'll come to a large ornamental pool that doubles as a water processing facility as well as a backdoor into Sanctuary's inner facilities. You can't miss it, it has a lot of greenery and flowers in addition to a dead Cerberus trooper floating facedown and a Harvester corpse. Use the water pump security panel to drain the pool, and head down the ladder. One of your squadmates will examine the strange machinery formerly submerged in the water, pointing out it has Reaper tech.

That said, go through the door on the former lake's other side. First room is empty except for possible additional squad comments on the Reaper tech. The second chamber has a couple of salvageables: equipment on your right (1,500 credits) and Rosenkov Materials Shoulder Plate to the left of the next door.

Some people are too confident on their Bond villain lair security measures, some are just careless

The next room is a command center and a squadmate tells you to turn on the power; to do so, use the computer in the middle of the room. You will see footage of Cerberus turning the refugees into husks. Shepard then walks to the other computer in front of the room's glass window to turn the lights on, leading to a view of the husk-infested facility beyond. The creatures quickly disperse: one gives a jump scare by creeping across the command center windows, though then again there's actually a bunch of them crawling Spider-Man style as the camera zooms out.

In the aftermath one of your squadmates could not fathom what Cerberus could possibly gain by making husks. Shepard reminds them the Reapers attacked Sanctuary because it became a threat, and it's your job to discover why.

In the next room there is yet another video console you can watch in the corner on the far end, it shows Oriana/Miranda shutting down the power and Kai Leng not too far behind her. Also in this room is a PDA log that explains about the "recycling" being performed.

Mere appetizers for the battles ahead

Go down the stairs and open the doors, but be prepared for a lot of husks. Unless you retreat, you'll basically face them in a flight of stairs - you going down, they going up - use it to your advantage. Below the stairs is another array of workstations, with two logs that explain something from Henry Lawson, Miranda and Oriana's father, about the deception. There's also 2 boxes of thermal clips and grenades for your restocking needs in addition to 2 more thermal clips next to a log.


The next room is a long hallway stretching to the right, divided lengthwise. It's the place you saw infested with husks earlier, right below the command center. The larger of the two spaces, (the one up the stairs) is more exposed, but the sheltered one (behind the door) is of lower elevation. Both of them are exposed to 2 unreachable platforms on the left side of the length of the hall, from which Marauders will spawn to shoot down at you. A Ravager is in the next room labeled "INCUBATION RESEARCH 02" and a Banshee spawns in the large overhead platform; both of them will proceed to the main area to hunt you down. The Reaper forces appear once you either open the door or climb the stairs, and the Banshee's distinctive screech more than confirms it.

Her literally dazzling looks is something NOT to die for

Honestly, your best bet might be to retreat back up the stairs you came from and camp: this will lure the Banshee and Ravager out of position, separating them from the Marauders and denying them their terrain advantage. The Marauders sometimes spawn at ground level instead of the platforms, although they may try to jump back to them. As the battlefield has a lot of waist-high obstacles, be wary of doing combat rolls back into one especially if the Banshee is almost upon you.

The room labeled "INCUBATION RESEARCH 02" has a med kit and 2 more logs from Henry Lawson, one of which is about Paul Grayson. Accessing the logs prompts a comment from one of your squadmates. You could see another Banshee behind a window, but it can't get to you as it's in a sealed room, so ignore it and go through the door on your right.

Search the Perimeter[]

There's another console with a Lawson daughter's voice coming from it. Watch her announce she's heading to the tower to disable the communications scrambler. To your left, you can pick up research data worth 1,500 credits. There is also a PDA here.

PROTIP: scope out and neutralize the purple glowing things BEFORE they become purple glowing things

Head up the stairs towards a two-door hallway. Prepare to encounter a group of Marauders and Cannibals, supported by 4 Barrier Engines. Try to deal with these from the doorway or a general distance; entering the hallway leaves you prone to being flanked. Three of the Barrier Engines can be taken out from the entrance area; two of them without spawning the Reapers, all 3 if you have wall-piercing guns. The fourth one is just too obscured at the far end of the room and will require you to come closer.

This large lab area details more of Henry's progress making husks, calling it "assembly-line science". The right side has the M-12 Locust, thermal clip and grenade boxes, and a Shotgun Blade Attachment. The left side has 2 logs. At the far left end is a PDA and another Lawson daughter console, containing evidence her father is working for the Illusive Man (in case you hadn't figured it out by now). You then get another clip of Henry and the Illusive Man talking about their experiments, which are about gaining control of husks, and they've made significant progress: indefinite short-range control, with controlling the Reaper ships themselves a considerable challenge but on the horizon.

With the link to Cerberus definitively established, you press onward. However there's one more scene on the screen: Kai Leng getting the drop on the Lawson daughter, with the video cutting off before anything else happens.

Unlike the other Lawson daughter consoles, this one is mandatory viewing. Climb up the ladder Shepard just lowered after the vid. This is a point of no return.

Fortified Ravagers[]

Reapers also know a thing or two about teamwork

Up the ladder is another double-hallway fight. An initial 2 Ravagers, 2 Cannibals and 2 Marauders (one near the Ravagers, one by the stairs nearest to your initial location) are backed up by 2 Barrier Engines nestled between the central support struts, one near you and one further up. When some of them die another 2 Cannibals and 1 Ravager emerge from the far end of the hall, and the room the Ravager comes from has another obscure Barrier Engine that's too hidden from your initial position even with sniper rifles (the Ravager will always get a barrier buff unless you somehow close the distance fast and shoot the Barrier Engine before it does its thing, feasible with a Vanguard or Infiltrator but a real high-risk low-reward scenario).

Move between cover spots, keep your shields up, and keep shooting. Keep in mind that squadmates may often walk straight into Ravager fire, so try to assign them to cover rather than risk them running about. Tip: If you have a penetrating ammo mod or a sniper rifle that comes with it built in, you can shoot the nearest and most dangerous Barrier Engine through the glass without coming under Ravager fire. You may then be tempted to follow up with some headshots to Cannibals, but don't give the Ravagers time to advance to the top of the staircase and trap you. Warning: Mind the Spore Pods along the south side (to your left from the entrance), they don't disgorge Swarmers but getting caught in acid explosions isn't any better either. The Gestation Pods farther along do spawn Swarmers and they're mixed in with some Spore Pods so also note the distinction, just give them wide berths, or shoot from a distance.

More Cerberus war crimes for the scales of judgment

You'll know everything's dead when the objective changes to "Search the Perimeter." There's only a thermal clip box in the first room and nothing else. In the second room is a grenade and clip box, a medical station, research data (3,000 credits), Henry's log explaining the Reapers realized what they're doing and attacked, another log releasing the husks in the inaccessible room (one is identified as a female refugee and still speaks...), and lastly one squadmate goes to the open door on the other side of the room and the other guy shouts it's a way out.

You emerge again at the cavernous hall the command center overlooks, this time on the same level as the overhead platform where the first Banshee came from. Jump across the gap to reach the platform. There's a power box at the front of the tank-object-thing you're standing on, right there on the floor; shoot the panel off and activate it. You may see a bunch of husks prowling or growling about but they won't bother you and you can't kill them anyway. Jump off when you're at the other side of the hall and go through the door. Time to fight again.

Final Battle[]

You nimble enough to evade rampaging Brutes?

The point of no return is when you drop down to the ruined section of the ramp from the door. Before you do so, you are given the opportunity to spy at the far end of the room: a Brute and a Banshee clobbering infrastructure.

Once you drop down, 2 Brutes spawn at the hallway in this last lab area. Similar three-tier battlefield layout as the one you previously fought in, except thankfully no Barrier Engines or exploding pods. Keep moving, but be careful how far you advance: the Brute/Banshee combo is a partial geography trigger, meaning you might fight all of them at once if you run too far up the hallway. If you already killed the first 2 Brutes, the last Brute and Banshee's attention will swing towards your direction regardless of where you are.

Thermal clip locations here are accessible enough, there's a single med kit at the upper tier, and if you use grenades there are pickups on the floor beneath a pod with a husk and another one by the hologram at the far end of the hall, so be careful not to incur the Brute and Banshee's attention if you're not ready.

Tip: It is possible to kill the Brute and Banshee through the glass with a good enough sniper rifle or powers that apply directly to the enemy (Combat Drone, some of the squadmates' powers like EDI's Incinerate and Overload, Liara's Warp, etc.), as soon as you enter the room, before even starting the fight with the two Brutes. Also note there are more places to run and dodge than is obvious at first glance - you are allowed to run on the diagonal glass windows directly to the right of the wrecked platform on which you enter the room, making this effectively a "three hallway" battle. Run around to stay at long range as much as possible while taking these enemies down, since they are all most deadly at close range.

Why is there a weapon inside a containment chamber is one of those Mass Effect mysteries that will never be solved. Along with random firecrackers or giftboxes at random locations.

When the fighting dies down one of your squadmates runs up to the elevator the Brute and Banshee were banging their fists on, then returns to you when you see it. Take your time to loot the place first though, there's no rush.

On the long table of workstations next to the elevator, some salvageable research data (4,500 credits). Aside from the combat supplies, the aforementioned hologram can be interacted with. It gives you the option to override a pod in the lab: the easternmost one (to the left, coming from the entrance to the room). Activate it to slide open the glass. Inside is the M-99 Saber.

Confront Henry Lawson[]

Save if you want before entering the elevator, it's the last time to do so on this mission. Just beyond the final door are ominous sounds of a shootout, however no one dies until you proceed.

Henry and Ori in a hostage situation at Sanctuary

You emerge on the topmost floor of the facility, once again overlooking the cavernous hallway where you first came in below. It's cutscene time on the other side, with Henry Lawson holding Oriana hostage. If Miranda is present, she'll be at the standoff as well. The choices you made throughout the previous events regarding the Lawsons' story will all boil down to this scene.

There are multiple potential outcomes:

  • If you ask about Henry Lawson's legacy, the camera will focus on the cracked glass behind him.
  • If you can't pass the Reputation check and "just want Oriana", you'll have a Renegade Interrupt option to wound her in the leg, distracting Henry:
    • If Miranda is present, she will slay her father via biotics and Oriana lives.
    • If Miranda is not present, Shepard can kill Henry with another Renegade Interrupt. Otherwise, Shepard will tell Henry to run away, letting him go.
  • If you don't take the Renegade Interrupt and Miranda is not present, Oriana will backpedal towards the glass and throw herself and her father down, which ends in both of them dying. If Miranda is present, she'll kill her father, but her father will also mortally wound her.
  • If you do pass the Reputation check, you'll be able to use a Charm/Intimidate option that gets Henry to release Oriana. If so, you'll get a Renegade option that allows you to kill him. If Miranda's present, she'll take it before you get a chance to.
Miranda's survival requires a specific set of spread-out conditions fulfilled, or in her favorite word, "perfect"

If Miranda is present, the following conditions will determine whether she dies.

  • If Miranda wasn't warned about Kai Leng, or if you didn't complete her Loyalty Mission, she'll be gravely injured and die at the end. Warning about Kai Leng requires reading the dossier on the assassin before speaking to Miranda over vidcomm, and completing her Loyalty Mission means you must have at least imported a Mass Effect 2 save.
  • If you break off a romance with her during Mass Effect 3 she will also die, regardless of whether you did both her loyalty mission and warned her of Kai Leng. Breaking off a romance during Mass Effect 2, even at the very end before importing the save, will not result in her death. A romanced Miranda will also survive if you have "locked in" another romance before the apartment scene—only an explicit "on-camera" breakup leads to death.
  • If you deny her access to Alliance resources during your third meeting, or if you never met for the third time on the Citadel, she will die.

Note: Miranda may appear wounded in the cutscene, but can still survive.

Whichever Lawson sister you've been chasing will disable the scrambling tower, allowing her warning to pipe out and guarantee that no one gets near Sanctuary. In the meanwhile, one of your squad members manages to salvage a little data to start you on your way to finding the Illusive Man.


The mission Priority: Cerberus Headquarters becomes available. If Miranda died in Mass Effect 2, Hackett will use the gathered data to track down Cerberus Headquarters. Hackett will add that the losses will be higher because the Illusive Man knows that they'll attack, though functionally nothing happens to War Asset ratings. If Miranda was present at Sanctuary, she'll confess she planted a tracker on Kai Leng that will take you there. It is also possible for her to tell you about the tracker and then die.

If Tali is alive and Miranda was present for the mission, then afterwards an intoxicated Tali will appear in the Port Observation Lounge, having acquired a new respect for Miranda. This will occur whether Miranda lives or dies, though with slight dialog variations depending on the outcome. Multiple factors will also influence the interaction: If Javik is around and the conflict between him and Liara was moderated after Thessia, if you visit Javik first or Tali first, and/or whether you're in a romance with Tali or not.

The Alliance Sixth Fleet will join the fight as a War Asset. If Miranda is alive, she'll also join the war effort.

If Miranda comes out alive in this mission, she becomes fully available for further interactions in Mass Effect 3: Citadel. As Citadel: Party requires the issues of its participants dealt with, after this mission Miranda's issues are solved and that mission can commence with all possible attendees.



Front Desk Log

Civilian processing ratios:
Adults, 60% sent to integration
Children, 85% sent to integration

Suitable candidates are being assigned to temporary living areas in alphabetical order. Family units are being preserved for ease of processing.


Personal PDA

Confirmed: unsuitable materials re-assigned to recycling.

Progress Update

Rejected subjects have proven useful for preliminary genetic testing. The death rates are 100%, of course, but the data being gathered is critical to improving subsequent testing on viable subjects.

Note: Only approved personnel with Alpha Three and above level security clearance are allowed access to the genetic waste testing area. Be aware that security breaches of any kind will result in immediate contract termination.

Internal Memo: Streamlining Procedures

In an effort to streamline our waste elimination process, a high grade liquefaction compound has been added to our alkaline hydrolysis disposal systems. Our goal is to ensure that our processing system can meet the expected processing ratios as more subjects arrive at this facility.

As a result, personnel must wear level-4 hazmat suits at all times while in the disposal area.


  • In the room where a banshee is trapped behind some glass, the only exit is a door that occasionally causes you harm when you try to access it. The only known fix so far is to restart the mission. To date, this bug has been confirmed for the PC, Playstation3, and Xbox 360 versions.[1]
  • After the last recorded message from Miranda, you climbed up the ladder and cleared the room of reapers. The game (on PC) can crash when going through the doorway at the end of this room. This is just before getting on the "tram" ride. A fix for this is to set the game to windowed mode and turn off both anti aliasing and dynamic shadows. You can now walk through the doorway and turn them back on. [2]


  • At the conclusion of the mission if Miranda doesn't die in Oriana's arms, Shepard's final line is "I've had enough of this place." This is similar to the line Shepard says at the very end of the mission on Horizon in Mass Effect 2 ("I've had enough of this colony").


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Priority: Thessia Missions Priority: Cerberus Headquarters