U.S. government agent Harry Hannan suffers a nervous breakdown after his wife Dorothy is killed, and spends five months in a sanitarium. Upon returning to his apartment in
New York City, he finds it is occupied by a doctoral student named Ellie Fabian. She explains that she had a sublet arranged while she was in the last semester of her studies at
Princeton University. Ellie claims that the housing office said the Hannans would be gone indefinitely. She gives Harry a note that was slipped under the door, but it contains only a few
Hebrew characters that he cannot read. Paranoid that he is being targeted by his own agency, Harry visits his supervisor Eckart, who assures Harry that the agency has higher priorities. Eckart insists that Harry is not ready to return to the field, but that he is perfectly safe. Harry takes the Hebrew note to a local rabbi who can only partially decode it, and explains that it means "Avenger of Blood.". The rabbi then calls Sam Urdell, and informs him that Harry has visited him. Harry notices that he is being surveilled, loses the tail and goes to the
American Museum of Natural History, where Ellie is working. He gives her some money and urges her to stay in a hotel, because he fears she will be accidentally targeted. He then visits his wife's grave, where he confronts her brother, Dave Quittle. Afterwards, Quittle visits Eckhart, who orders Harry's murder. Ellie stays in the apartment despite Harry's request. Ellie suggests that they take the note to her friend at Princeton who specializes in Hebrew studies. When Harry wakes from a nightmare, he tells Ellie about the death of Dorothy. He takes a prescription pill, but spits it out, realizing that it is cyanide. The next morning, they leave for Princeton. On the train, Ellie tells Harry about her grandmother, when Harry notices Quittle, and an old man, watching them. At Princeton, Richard Peabody decodes the note for Harry. Peabody has accumulated several notes, all attached to very peculiar murders. Harry is the first one to have received the note and lived. He also relays a message that someone wants to meet Harry in the bell tower courtyard the following day. In the courtyard, Harry is lured into a trap by Quittle. Harry manages to kill Quittle during a shootout in the bell tower, and then encounters Sam Urdell, the old man on the train. Sam explains that he is part of a committee investigating the blood murders. 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. As she has sex with Meckler, she drowns him. As Harry and Sam put together their information, they are led back to Princeton. Harry realizes that Ellie is the one murdering men, all of whom are descendants of members of
Zwi Migdal who had sex trafficked her grandmother. They drive up to Niagara Falls, where they have an emotional confrontation. She tries to kill him, but confesses that she loves him. He is conflicted, but he tells her that he will turn her in. Ellie runs from him, and he chases her through the
Robert Moses Niagara Power Plant. She escapes onto a tour bus and he steals another tour bus and follows her to the
Cave of the Winds, where he chases her through the tunnels until they have a final confrontation at the edge of the falls. They break through the railing and Harry grabs Ellie, but she struggles and takes a deadly plummet. ==Cast==