Simon Killer is the story of Simon who travels to the city of love, Paris, after his five year relationship with his girlfriend (never seen or heard on screen) ends. The collapse of the relationship has seriously affected Simon and seems to have both emotionally and mentally affected him. This is the backdrop for the film, which in all serious, is a study in madness; we watch, over a period of a few months, how this dark depression can turn a man into a killer.