One of the few missions you can undertake before completing Priority: Palaven, you’ll unlock this mission when you talk to Specialist Traynor on the Normandy, after your first visit to the Citadel. Note that in Mass Effect 3 the N7 missions are effectively multiplayer maps turned into small, condensed missions. There’s also usually a mission item you can find on each of these N7 missions, which is required to complete another side mission - in this case you’ll want to look out for a Failed Medi-Gel Experiment, which will start the mission [Citadel: Alien Medi-Gel Formula]. We will, of course, point these out to you.
To start this mission, travel to the Decoris system in the Sigurd’s Cradle cluster and land on the planet Sanctum. Upon starting the mission, go inside to your left and scan the console for 3,000 credits; if you then look left there’s a room just up the ramp and to your right. Inside here there’s a Failed Medi-Gel Experiment you can collect for one of the Citadel’s side missions a bit later on.
Double back out to where you were dropped off and run up the ramp opposite; tucked away in the corner of the archway (on the floor), you’ll find a Sniper Rifle Enhanced Scope to pick up. Be quick, then take cover before a shootout takes place.
Most enemy fire will come from your upper-right side, so pick these guys off from a distance where possible. Use your team’s biotic powers to maximise the damage dealt and when it’s all clear, it’s time to do a spot of item collecting.
Pick n Mix
To the right of the entrance you just came in is a terminal you can scan for 3,000 credits , and around the corner to your left there’s a Medical Station for XP or Medi-Gel. In the upper-left corner there’s a journal entry you can read for 18 XP and in the far right corner (where the troops previously were), there’s another terminal hiding 4,000 credits from you.
Now go to the terminal holding the containment system and activate it to release the Reaper artifact. Take this back to the ship and head back inside via the right door.
Stand behind the glass panel as this provides cover overlooking the location of where the Engineers (there’s two of them here) will always attempt to leave a turret (Engineers can also repair damaged turrets or even replace destroyed ones). When you see an Engineer, make them a priority target! You can sometimes prevent turrets being placed by killing these guys quickly enough.
More troops will convene at this location, so be ready to either pick them off at a distance, or wait for them to come up the nearby ramp and get close. If a turret is dropped, stay in cover and pick it off with powers as it can mow you down in mere seconds.
Once the coast is clear, you can scan a terminal in the right-hand corner for a journal entry worth 18 XP , then activate the containment system bypass terminal. This time, a couple of Assault Troopers will come in from above, so take cover and pick both of them off.
There will also be additional Cerberus troops inside the base now, so after grabbing the second artifact, be careful as you make your way back to the landing pad.
You need to hold off the Cerberus assault as they send in Engineers, Guardians, Centurions and Assault Troopers to your location. A good idea is to head outside now and take up position near the top ramp (having your team covering the door to your left), meaning that once Cortez arrives, you can just make a dash for it to end the mission.
Be careful though, each change in dialogue with Cortez means a new wave of tougher enemies will start showing up. When the Engineers begin turning up, you’ll know that you’re now not too far from the ship arriving. Once it’s here, you only need to press the action button at the door to complete it. A successful mission will earn you +5 Reputation points and 10,000 credits .