Danger Zone (1951)

Claire Underwood hires San Francisco private-detective Dennis O'Brien to purchase a saxophone case at an auction, and O'Brien is promptly slugged and the case is stolen by Larry Dunlap. O'Brien snoops around and learns that Claire and Dunlap are rivals in a smuggling racket, and he seizes Claire just as she is about to leave the country with the case and its stolen jewels. O'Brien then gets involved with the murder of Vicki Jason's husband and gets slugged again and framed. With the aid of "Professor" Schickler, he proves his innocence when Vicki kills her co-conspirator lover, Edgar Spadely---another private-detective who had gotten O'Brien involved to begin with---and Vicki admits her own guilt in the murder of her husband.