Ex-cop Valentine 'Mac' McGrath is now a private investigator.Hired to trace a missing teenage girl, who is subsequently found murdered, Mac becomes embroiled in the hunt for a repeat killer who is tagged the Saturday Night Strangler.Following a hunch, Mac unwittingly comes to the attention of the depraved psychopath and his newly acquired partner in crime, and they decide to eliminate him.Maggie Connelly is an artist, lives on a canal boat, and has fallen in love with Mac, having been there for him since her best friend - Mac's late wife and son were killed in a car crash.Mac's involvement in the case leads him on a course that will bring him and the killers face to face.