He was kidnapped by the Reapers and his wife, Lynnae Carey was murdered in an alley. Brandon is taken to the sewers so the Reapers can control them.
DARPA operative Moya Jones sends her temporary partner, Cole MacGrath, to find him. He uses his Psychic Vision for the first time in this mission, entitled Blood Trail. He experiences Lynnae's death and follows Brandon's residual neuro-electric energy to his hiding place in the sewers. Scared that the Reapers will murder his wife, he will not let Cole in, and here a Moral Choice occurs:
Cole can zap him, opening the door.
Cole tells him about Lynnae's death. He grieves and opens the door telling Cole to kill every last Reaper. He then sits in a corner.
Both choices let you through the gate no matter what.