Peter gets Nikki/Jessica's split personality 'power.'
Peter accidentally gets Candice's power in season 1 finale while she rescues Sylar.
Nathan saves New York, dies in the explosion.
Peter is distraught at killing his brother, researches why Linderman/his mother/the company was rigging Nathan's election. Finds their true motives + things they did in the past. During this investigation he meets the Irish brotherhood, falls in love with the girl, gets lightning power. Discovers past job that they did, knocking over shipping container of iPods.
Split personality 'power' kicks in, the murderous-get-the-job-done side takes over, time travels to the moment of the explosion, grabs himself after he heals from the explosion, erases his own memory with the Haitian's power, locks himself in shipping container that he knows the Irish are going to rob to protect himself, yet to keep himself out of the way. (Possibly leaves instructions for himself in the box? Who erases your memory then gives you a box with your identity in it unless it's for a reason?)
Peter then assumes Nathan's identity, alienates himself from Nathan's family, including Claire. Starts his vendetta against the 9 people (theoretically everyone left alive who has worked in a management type position for them, since HRG is included in the paintings).
START SEASON 2
Peter bumps into Ando and puts the marked picture into the newspaper.
Peter goes back home and places the marked picture of his mother there for her to find when she leaves.
Talks to Claire, tells her to stop calling, he doesn't have any answers for her. Looks into the mirror and sees a scarred face of Nathan, presumably as guilt for killing him in the explosion.
Peter kills Hiro's father.
Attacks his mother with his new lightning power while she is in jail, causing the lights to flicker, but is unable to kill her because his 'good side' takes back over and he flees before Parkman can break the window.