In a brilliant yet rather difficult tale, the Red Universe Fringe Division uses a distinguished forensic psychologist from the Blue Universe to capture the psychopathic version of himself, a gruesome serial killer.
The sense of dread from the very simple, but real possibility, that everyone has murder in them - it's just a matter to push the right triggers - takes over one John McClellan as he questions the very nature of his existance, as well as a most debilitating reality: he can't save himself.
To embrace these murders, to make sense of them, became as important for one McClellan as it was for his counterpart to stop them, the trophies guarded in the name of science as compelling as the one the killer kept from his victims, there's no difference between them, just a point where their paths diverged in directions in which both of them excelled at. As it turns out, this point was happiness, a simple moment of acceptance one experienced as a child where the other one didn't.
The grown up psychopath steals that memory and becomes the man he never had the chance to be, a man willing to kill himself for all the suffering he caused. The memory gone, the path still intact, a forensic psychologist only has the shadow of a feeling, from a moment he no longer remembers he experienced, to hold on to ...with both Universes paying that would be enough for him.