Billy Pettigrew is a Scottish geologist who worked in Fortitude, responsible for the discovery of the preserved mammoth carcasses on the glacier.
Little is known of Pettigrew's background, but is is suggested that he is a well seasoned traveller, having lived in many countries before settling in Fortitude.
In the opening of the first episode, Pettigrew is shown being eaten alive by a polar bear along the Svalbard coast. He is then shot by Henry Tyson, who was taking photographs in the area. It is implied Tyson was aiming for the bear, not Pettigrew.
It is revealed through various flashbacks throughout the season that Pettigrew was close friends with Yuri Lubimov, and had a hostile relationship with Officer Eric Odegard, believing him to be emasculated by working for his wife. Pettigrew shared with Yuri he had discovered something beneath the ice, but was unspecific about it being a mammoth graveyard. At some time near Christmas, Pettigrew gets into a fight with Eric, and after being beaten returns to the Midnight Sun Hotel and asks Elena Ledesma to bring some ice to the room. When she obliges, he then secured her to the bed with Yuri's handcuffs and attempts to rape her. Elena is able to stab him and call Sheriff Dan Anderssen for help, but by the time he arrives Pettigrew has already raped her.
Due to his infatuation with Elena, an infuriated Dan handcuffs Pettigrew inside his patrol car and drives to the coast. During the drive, a drunken Pettigrew rants about how he and Dan are the same, and he did to Elena what Dan wanted to do. Furious, Dan handcuffs Pettigrew to a pylon with Yuri's cuffs, and waits in the car until he is attacked by the polar bear. After dismissing Henry Tyson after he shoots Pettigrew, Dan removes his severed arm from the cuff and places it with his corpse.