Peter was one of the survivors of the undead apocalypse who took refuge in a secluded shopping mall.
Peter and Roger were part of a SWAT team who are sent to attack an apartment building where the tenants are not bringing out their dead. When Wooley, one of Peter's fellow SWAT troopers, goes berserk and starts gunning down both zombies and innocent bystanders, Peter kills him and follows Roger into the basement.
Peter and Roger agree that the zombie apocalypse will only get worse, and decide to abandon the SWAT team and join Stephen and Francine. A priest then comes in and allows Roger and Peter to "do what they must." The two then kill all the zombies kept in the building's cellar.
Roger and Peter meet up with Fran and Stephen at a deserted police station on the Delaware River in time to save the two from four rogue cops. Peter is allowed to join the group, and the four spend all night flying around in the helicopter. In the morning, they arrive at a secluded airport to refuel, and are attacked by zombies which Roger and Peter successfully kill.
The group eventually reaches a secluded, zombie-infested shopping centre, where they land on the roof and break in through the skylight to rest and collect supplies. Peter and the group race around the mall, collecting supplies, which they take to a zombie-free upstairs area. When the group decides they need to clear the mall's zombie infestation, Roger and Peter go out into the zombie-infested parking lot and hotwire semi-trucks from a nearby warehouse. They use these trucks to block off the mall entrance, but not before Roger is bitten.
Stephen, Fran and Peter care for the ailing Roger. Meanwhile, the group makes the mall their home, and Peter places a fake wall over the stairwell leading up to the office area to hide it from any potential intruders. Roger makes a last request to Peter to kill him if he comes back, moments before he dies. Roger's corpse reanimates, forcing Peter to kill him. The group then buries Roger's body.
Peter and the rest of the group begin to bicker as their sense of isolation strengthens, and the mall transforms from their utopia to their prison. That night, when looters and thousands of zombies break into the mall, after Stephen is killed and turns, Fran and Peter retreat to the upstairs, office-like area.
Peter convinces Francine to go without him, and stays behind with a gun to his head. However, at the last second, as zombies pour in, Peter changes his mind and escapes onto the roof and aboard the helicopter with Francine. As zombies pour out onto the roof, Peter and Fran leave the mall in the helicopter, and fly off into an uncertain future.
In the original script, Peter did indeed shoot himself after Francine escaped onto the roof.