A detective investigating a series of murders becomes involved with a woman who may be the culprit.
 
This is a pretty decent "who done it" serial killer movie. 
 
FUN FACT:  Included in the final cut of the film is a scene where Al Pacino's character gets rudely bumped into on 5th Avenue while trying to court Ellen Barkin's character. According to director Harold Becker, this was an unscripted moment caused by a real New Yorker, and not an extra. Pacino incorporates the moment into his performance, and continues without missing a beat.