Collects Ultimate X-Men #13-25. Featuring many key introductions, including Proteus (the evil son of Professor X), the fan-favorite Gambit and Jean Grey's dark alter-ego, Phoenix. The X-Men are cut to the emotional core as they battle their way through an obstacle course of deadly trials. First, Professor Xavier is forced to confront his past sins when his own son explodes into a destructive force. The question is, will he sacrifice his team to save his son? Then, the X-Men face another internal conflict when Jean Grey turns to the dark side. To save themselves, and the world, will the X-Men strike down their own teammate?