Collector Base: Infiltration

In order to reach the main control chamber, the assault on the Collector Base has been divided into three teams. One team member is proceeding through a ventilation shaft while two teams distract Collector forces.

Acquisition
This mission is triggered as part of the Stop the Collectors: Defeat the Collectors mission, once you have managed to pass through the Omega 4 Relay and have crash landed on to the Collector's base.

Illusive Man Briefing Pre-Relay
This mission begins with the trip through the Omega-4 relay. The Illusive Man will brief Shepard (who is in full armor) and tell you that he doesn’t know what to expect on the other side. You will then be treated to a long cutscene where your decisions on ship upgrades will play out.

Debris Field
The enormous wreckage field into which you emerge testifies to the number of ships which have tried, unsuccessfully, to travel through the Omega-4 relay. Joker manages to maneuver the Normandy around the debris but EDI will warn that there are enemy vessels approaching. Joker takes evasive maneuvers as they open fire on the Normandy’s upper hull. If you failed to upgrade the Normandy's armor, then an Oculus laser will penetrate the Normandy's hull and kill Jack.

A pursuing Oculus will punch through into the Normandy’s cargo hold. Shepard takes two squadmates down to deal with it. Shooting from cover, keeping your squad mates in cover, and frequently changing position tends to be the best tactics, as the Oculus will constantly pursue you and will also try to flank you. Be careful of the large number of explosive canisters around as they will not affect the Oculus but they can be deadly to you and your squadmates.

About halfway through the battle a cutscene will play where Joker has to lose the remaining Oculus chasing the Normandy by sending the Normandy through a field of debris. If you didn’t upgrade the Normandy’s barriers you will lose a squadmate here when the Normandy's drive core overloads. Eventually Joker emerge from the debris field with the remaining Oculus destroyed, save for one which re-enters the cargo hold. Joker comments that “It’s Shepard’s problem now”. You will return to the cargo hold where the Oculus returns and continues the battle, with full armor, regardless of how much damage you inflicted before the cutscene. Once the Oculus is destroyed Joker will call you back up to the cockpit where the Normandy is exiting the debris field.

The Collector Base will come into view and it launches an old friend - the Collector Cruiser - which turns to face the Normandy. If you upgraded the Normandy's weaponry, then the Normandy will easily dispatch the Collector Cruiser at range. If not, the Normandy must engage it at point blank range with conventional weaponary and the ensuing dogfight will lead you to lose a squadmate.

Once the Collector Cruiser is destroyed, the resulting explosion overloads the Normandy’s systems and forces Joker to crash-land the ship. Shepard asks if the Collectors can detect them, and EDI replies that this is unlikely because of the lack of an internal security grid - the Collectors probably did not expect anyone to get this far. It is time to infiltrate the base to stop the Collectors, once and for all.

Mission Briefing
Shepard and the crew gather in the Normandy's briefing room, while EDI projects a scan of the Collector Base and comments that the station’s weak spot is likely in the main control center in the center of the station. EDI also says that this is the likely location of the Normandy crew and any remaining colonists. There are two ways to get to the center of the station, but a specialist must pass through a thermal vent in order to get the two squads through to the next area of the station.
 * Ideal: Tali or Kasumi
 * Non ideal: Anyone else, as they will be shot attempting to close the doors.

Once the choice is made, Miranda will say that while Shepard will lead one squad, someone else must lead a second squad to serve as a diversion. She volunteers to do so, but you can choose any other squad member.


 * Ideal: Garrus, Miranda, Samara or Jacob.


 * Non Ideal: Anyone else

Once that choice is made, you have the opportunity to make a rousing speech to your troops. Select your own squad from the remaining members. The team then disembarks from the Normandy and enters the station.

Thermal Vent Gates
The initial area is clear of Collectors but once you reach a fork in the road the Collectors swoop in, so take cover and prepare for a fight. Your Tech specialist will move through the thermal vent, but will inform you that there are obstructions in the way preventing them from proceeding. These obstructions are valves which can be opened by pressing green buttons found throughout the level.

After removing the first obstruction, a bar will appear in the lower right of the screen showing how much time the specialist has. If the bar runs out then the mission ends in a critical mission failure as the specialist gets fried. On higher difficulties, it is hard to take the Collectors out fast enough to prevent a heat buildup, so on some occasions you will have to activate the gate controls while under fire.

The next two valves are guarded by two sets of three Collectors, one of which will always be immediately possessed by Harbinger. Once you activate the fourth gate move fast and you will emerge onto more platforms. More Collectors will swoop in and attack. Take out the Collectors and move to activate the fifth gate. The sixth gate is down the hall and requires no fighting. Activate it and move on. There will be three Collectors around the corner; eliminate them quickly while they are clustered, then climb into the final room.

This next area is the hardest of this mission. There are two gates, a time limit, and two waves of Collector Drones, Assassins and Harbinger between you and finishing this mission. The seventh gate is easier to get to so if you are having problems taking out the Collectors then you will be best to leave your specialist there until the last minute. The initial group of Collectors will be replaced by a second wave that flies in, so if you're strained for time make a break for the final valve release while the Collectors fly in. Once the final gate is open, regardless of any remaining enemies, the mission will end.

The diversion team will charge into the safe area and attempt to hold their ground while the tech specialist opens the door to let in Shepard's squad. Once Shepard and the squad get in, the specialist will attempt to close the door again. If you chose an ideal specialist, the door will close. If not, the specialist will manage to close the door but will be shot dead before finishing the task. Also, if you chose a non-ideal second fire team leader, the specialist will still be shot, even if loyal and ideal. The room you enter holds a secret.

Enemies

 * Collector Drone
 * Collector Assassin
 * Collector Guardian
 * Harbinger