Hunter’s archenemy, a Soviet agent and killer known as Bluebird, is suspected of killing an American who betrayed the Soviets after leaking American nuclear secrets to them.

A Soviet double of Hunter – created through the use of plastic surgery – arrives to carry out a plot to kill General Baker and frame Hunter for the murder. But first he has to fool Marty into believing that he is the real Hunter.

A mad scientist programs an American agent to kill Hunter. He then arranges for Marty to have a car accident so that he can treat her for her injuries and uses the opportunity to program her to kill her uncle, an influential admiral in the United States Navy, when she gets the news that Hunter is dead.

After a hitman dies during a car chase, Hunter switches wallets with him, takes his place, and sets out to find out who hired the hitman and who the hitman's target was.

After a witness for a United States Senate committee investigating a connection between organized crime and a U.S. government intelligence agency (the fictional "GIA") is murdered, Hunter and Marty face the challenge of convincing the last surviving witness that they can protect him if he testifies.

Hunter becomes a wary ally of an East German spy who shot his fiancé to death nine years earlier. After the East German is killed at a film festival in Los Angeles, Hunter and the agency try to figure out who killed him.

When Hunter, Marty, and Baker try to stop renegade American agents from assassinating a United States Government official, Hunter's adversary, seeking political asylum in the United States, offers to betray the group that hired him to assassinate the dignitary.

Dr. Martin Reed, a chemist working for the U.S. government, disappears mysteriously. At the same time, Dr. William Maklin, one of his associates, is killed in a plane crash. Investigating Maklin's death, Hunter discovers that Reed is in hiding and plotting to poison the Southern California water supply and kill two million people if he does not receive a payment of $10,000,000 within 48 hours.

When Hunter helps with the exchange of a U.S.-held Communist spy for a Communist-held American spy – who happens also to be his favorite instructor in spycraft – persons unknown intervene in the exchange and kidnap both of the spies being exchanged. Hunter and Marty are assigned to find the missing American spy, and Hunter begins to suspect that a traitor in his own agency is responsible for the kidnapping.