In a Mexican cantina across the border from El Paso, 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. Dorothy is killed in the attack, and he suffers a nervous breakdown. Harry spends five months in a Connecticut sanitarium before being released.
On his way back to New York City, Harry stumbles and nearly falls into the path of an express train. He goes to the makeup counter at Macy's to retrieve his next assignment, but the assignment slip inside the lipstick case is blank. He accosts his contact who assures him that the agency probably does not have any work for him.
When Harry returns to his apartment, 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 notices that he is being surveilled, loses the tail and goes to the American Museum of Natural History, where Ellie is working.
He gleaned information about her from their brief encounter. He gives her some money and urges her to stay in a hotel, because he fears she will be accidentally targeted. Ellie stays in the apartment despite Harry's request. 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.
Harry takes the Hebrew note to a local rabbi who can only partially decode it. The rabbi informs the agency that Harry has visited him, and Eckhart orders Harry's murder. Ellie suggests that they take it to her friend at Princeton who specializes in Hebrew studies. On the train, Harry notices an old man and another agent looking at them.
At Princeton, Richard Peabody decodes the note for Harry and explains that it means "Avenger of Blood." Peabody has accumulated several notes, all attached to very peculiar murders. Harry is the first one to have received the note and lived.
The next day, Harry is lured into a trap by the other agent, David Quittle, who is the brother of Harry's late wife, Dorothy. Harry manages to kill Quittle during a shootout in a bell tower and then encounters the old man from the train, Sam Urdell. 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, on behalf of victims of white slavery like her grandmother. He drives 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 in the final shot there is a prolonged chase through the hydroelectric power plant. It ends above the falls, where Harry grabs Ellie, but she struggles and takes a deadly plummet.Roy Scheider as Harry Hannan
Janet Margolin as Ellie Fabian
Christopher Walken as Eckart
Sam Levene as Sam Urdeil
John Glover as Richard Peabody
Marcia Rodd as Adrian
Andrew Duncan as Bernie Meckler
Charles Napier as Quittle
David Margulies as Rabbi Drexel
Vincent Canby in a May 4, 1979 New York Times review of Last Embrace wrote of Scheider: "No other leading actor can create so much tension out of such modest material."