When a double agent called Kane is horribly disfigured in a chase, he vows vengeance...and calls upon the powers of a force who has tangled with Steed and his associates twice before: the Cybernauts. Creations of a misguided and imbalanced scientist, Dr Armstrong, these metallic menaces in both their attempts were stopped by the suave Steed and the inimitable Mrs Peel. However, this time they are being manipulated by an even more malignant force, and Steed and his friends enter into great danger in an attempt to stop the Cybernauts one last time.

Gambit tries to meet Travis, a man carrying some secret film, but he is killed before handing it over.

Having witnessed a test on a new sleeping gas called S-95 & thus made immune to its effects, the Avengers awake one Sunday morning to find the whole city of London asleep and an open house on the city's banks and jewellers.

Everything Steed cares about is being destroyed or threatened, including his china, his car, and even Purdey. The trio must uncover who would bare such a long-lasting and jealous grudge against the unflappable agent.

After Purdey is kidnapped, Steed is given the ransom of Allied attack plans. But has the whole thing been a set up to make the Ministry think Steed is a traitor?