The Avengers

Following the death of his fiancee Peggy at the hands of heroin smugglers, Dr David Keel vows to track down the killers and avenge his lost love. He is aided in his quest by a mysterious stranger, John Steed.

Steed has infiltrated a gang, led by Mason, which is implicated in Peggy's murder. Steed asks Keel to establish contact with a rival gang, and the doctor discovers that Vance's hitman, Spicer, has been sent to kill Steed.

Steed impersonates Riordan, a forger soon to be released from prison, and gains the trust of gang-leader Hooper. Things seem to be going well until Hooper's second-in-command, known as the Cardinal, announces that Riordan's girlfriend is outside waiting to see him.

Keel receives a 'phone call from one of his patients, and ends up assuming the identity of her missing husband, a scientist engaged in secret research. Shot in the chest, Keel needs a minor operation - but the anaesthetist has tampered with the oxygen.

A young girl, Carmelite Mendoza, has been kidnapped from a Caribbean island, but Steed suspects a political motive. His suspicions are confirmed when Vasco, the Mendoza family retainer, is observed killing the original kidnapper and abducting the girl himself.

Keel, reviving a young woman who has jumped into the Thames, is led to the Radeck State Circus, where the trapeze girl is guarded, her face covered by bandages because of an accident. The 'trapeze girl'proves to be the daughter of a defecting scientist, who will be used to force her father to return home. When Keel discovers this, he and Carol are captured by Zibbo the Clown, who will shoot Carol if the police investigation is not called off.