It took me about 90 minutes on normal difficulty. Admiral Hackett asks you to rescue a covert operative who is his friend in a Batarian system. You go by yourself to rescue her. When you rescue her you find out they found a reaper artificat on an asteroid in the system and discover the reapers will use the mass effect gate in this system to invade, its some kind of "alpha" gate. The invasion will begin in a little over two hours.
The original plan was to push an asteroid into the gate to destroy it, kind of like the DLC brink down the sky. The spy takes youto the asteroid to see the artificat because you want more proof. You then find out the artificat has corrupted everyone on the asteroid and you are betrayed. After a battle in the artifact room against the turned guards the artifact knocks you out with some kind of energy pulse. Everyone on the asteroid is working for the reapers. You escape and attempt to start the engines on the asteroid to ram it into the gate. You start the engines after preventing the one you rescued from sabotaging the engines. Before you leave the asteroid either the collector general talks to you through a hologram (if you complete before the suicide mission) or you talk to a reaper (if you complete after the suicide mission)
The asteroid destroys the gate but as the gate explodes it causes a super nova and you kill all 300,000 Batarian colonists in the system. You didn't have time to warn the Batarians. Renegade or Paragon, it doesn't matter, you have no choice. Admiral Hacket visits you and says even though he agrees with what you did, 300,000 for trillions, after this is all over the alliance will try and put him on trial. End of DLC.
