Nunnaly is missing, of course. In her place, Lelouch has a brother, Rolo. He's obviously a spy of some sort.
He is the pilot of the experimental Knightmare. And he has a geass of his own.
Meanwhile, the Emperor shows Suzaku his secret: the Sword of Akasha: a weapon to kill God.
Lelouch has a crisis of confidence: with Nunnaly doing the SAZ, his campaign directly opposes her. But she's the reason he became Zero in the first place!
Strong words from Kallen and Rolo help him reorient.
He bails out the Knights, then orders them to cooperate with the SAZ.