Campbell is a vampire and he is working for Mitchell. He takes part at the AA meetings of Mitchell. He lives a long time without blood. Thats why his old memories come back. He remembers his victims and his last girlfriend. When he was newly-infected, Campbell had tried to turn his girlfriend into a vampire, but at the time nobody had told him how to recruit. As a result, his attempt failed and he killed her. For a long time afterwards he tried not to think about her, but when the Bristol vampires under Mitchell's leadership gave up blood, Campbell found his memories of her death returning.
He talks to Mitchell about this new feelings and tells Mitchell that he does not know how how to deal with this. Mitchell explains that these feelings are normal and that Campbell should try to deal with them.
It is not known whether Campbell was one of the vampires that died during the explosion at the B. Edwards or not.