A very smart Larry Cohen script benefits here from spot-on casting, as a cop-turned-writer and a hitman team up to go after a crooked politician, with the killer constantly egging the author into writing a book about him.
The clever premise fits in with a very neat plot, but the main reason the film works is that Brian Dennehy and James Woods two of the best and least well-used actors in American movies play so well off each other, Dennehys bearlike integrity neatly matched by Woods rattily confident psychosis.