[4] Very loosely based on the novel The 13th Man by Murray Teigh Bloom, it stars Roy Scheider and Janet Margolin.

In a Mexican cantina across the border from El Paso, Texas, government agent Harry Hannan is romancing his wife, Dorothy, when he observes an informant he is supposed to meet in a few days.

Realizing he is about to be attacked, he shoves his wife to the ground and starts shooting at the informant's companions who return fire and flee the restaurant.

Harry takes the Hebrew note to a local rabbi who can only partially decode it, and explains that it means "Avenger of Blood.".

Harry notices that he is being surveilled, loses the tail and goes to the American Museum of Natural History, where Ellie is working.

Harry manages to kill Quittle during a shootout in the bell tower, and then encounters Sam Urdell, the old man on the train.

They investigate the various clues, and they piece together that Harry's grandfather owned a brothel on the Lower East Side of Manhattan.

In a hotel at Niagara Falls, Ellie is dressed as a prostitute and lures Bernie Meckler into a bathtub with her.

Vincent Canby in The New York Times wrote of Scheider: "No other leading actor can create so much tension out of such modest material.