Priority: Rannoch

Acquisition
To acquire the mission, you must first complete either Rannoch: Admiral Koris or Rannoch: Geth Fighter Squadrons to trigger Admiral Raan informing you of the Reaper Base. To start the mission, orbit Rannoch and select the Reaper base.

Mission Summary
The Reaper base controlling the geth has been located, but jamming towers prevent conventional orbital bombardment. Land on Rannoch and use a prototype targeting laser to enable the Normandy to destroy the Reaper base.

Walkthrough
Upon arrival at the Reaper base, your squad will be attacked by several geth hostiles: five initial Geth Troopers and a second wave of either Geth Troopers. Elimate them and proceed down the hill. Once you near the bottom, the large blast door will close and three more Geth Troopers will drop down to impede your progress. Make short work of them. Check near the inside-right of the blast door for a SMG High Caliber Barrel upgrade.

Move to the right of the blast door near the tubes and vault up them. Climb the ladder and eliminate the Geth Trooper waiting at the top. Vault onto the pipe and move forward. Eliminate the two Geth Troopers and Geth Rocket Trooper, and move along the right side to their position. Eliminate the Geth Rocket Trooper on the catwalks in front of you, proceed to the ladder, and climb it. Climb up the pipes to the next level.

Eliminate the geth patrol below you consisting of two Geth Troopers, and find cover. Four Geth Rocket Troopers will drop in, and once they have been eliminated another four Geth Rocket Troopers will siege your position. Once all hostiles have been eliminated, press forward and through the doors. Salvage the Reaper tech on the right for 10,000 Credits.

Proceed up the ramp and destroy the lone Geth Trooper. A blast shield will expand over the Reaper tech broadcasting the signal. Proceed to the right. As you move along the linear path, numerous hostiles will attempt to impede your progress. Fight your way through the geth forces: two Geth Rocket Troopers, eighteen Geth Troopers. Once all hostiles have been eliminated, the geth VI will ask if you need assistance. Grab the Geth Plasma Shotgun and salvage the data (5,000 Credits) on the left of the door.

Move through the door and salvage more data for 10,000 Credits. Proceed through a second door and a nav-point will be marked on your heads-up display. Hostile geth will filter in from the left and the right. Eliminate all hostiles before activating the Door Override. Geth will filter in from the left side; once all hostiles have been eliminated, the geth VI will inform you that a manual override is needed and will mark a console on your heads-up display with a nav-point. Proceed to the nav-point and activate the Door Override. The geth VI will inform you that you cannot double back, but you can use the elevator marked on your heads-up display. Move towards the elevator, but be ready. When the elevator lowers, a Geth Prime will be riding it; eliminate it and the two Geth Rocket Troopers that drop down before boarding the elevator.

Ride the elevator up to the next level and be ready for a fight. Three Geth Primes will be standing with their backs to you: one on your left, one on your right, and one straight in front of you. There is a Geth Spitfire sitting on a crate before you, as well; grab it. Eliminate the three Geth Primes and then proceed to the nav-point. Shepard will pull the laser designator from his back. Designate the target by holding down the trigger. Once designated, the Normandy will proceed with its bombing run. The explosion knocks Shepard and his squad off the upper-platform, and a Reaper begins to climb out of the hole.

The geth VI tells Shepard that it has acquired transport. Sprint to the geth ship. Shepard will get on top and man the turret while his squad gets inside, the geth VI piloting. With the ship on the move, target the Reaper off to the left of the ship while Shepard calls in for an orbital strike. When the orbital strike hits, the Reaper goes down temporarily while Shepard orders EDI to sync the quarian fleet to the Normandy's targeting systems. Determined to take down the Reaper, Shepard stays back while the geth VI retreats to a safe distance with Shepard's squad.

Move to the center of the plateau and aim at the Reaper. A set of rotating targeting circles will appear. Begin targeting the Reaper by aiming and holding down the trigger. Once the orbital strike hits, the Reaper will move closer. Its beam will begin to charge. Be prepared to dodge to either the left or the right. Once the beam has made it's way past you, the circles will appear again. Begin targeting, and if you cannot fully target the Reaper at one time, dodge its beam and continue to target.

Another orbital strike will hit the Reaper, damaging it some more. You must do this one more time before the Reaper becomes too close to dodge. As the Reaper approaches you, the circles will appear again. As soon as they do, begin targeting the Reaper. Time will slow down momentarily as you target it's charging beam. Aim as close as you can to the center.

If you do not begin targeting earlier than when it reveals the eye, you will not survive the final salvo.

Once you complete the targeting procedure, the game will cut to a cutscene of the quarian fleet firing upon the Reaper. While it is disabled, it will speak to Shepard about Harbinger and the inevitability of Shepard's defeat. You will then be able to choose to allow the geth VI to upload the Reaper code to all remaining geth, or to allow the geth to die.

By choosing to upload, you get one last chance to stop the geth VI. If you choose to allow it, the geth VI will sacrifice itself and the upload will be finalized. The quarian fleet will be destroyed as the geth defend themselves, Tali will commit suicide, and Shepard will gain the geth as a War Asset. If you choose stop it, the geth VI will attack Shepard, dangling him over the cliff. Tali stabs the geth VI in the back, releasing Shepard and the quarian fleet destroys the geth and you gain the quarian fleet as a War Asset.

By choosing to allow the geth to die, the geth VI will attack, forcing Shepard and Tali to kill it. The quarians continue their bombardment of the geth fleet, destroying it.