When murderous fishermen kill an agent investigating an island, Steed, Gambit, and Purdey go to investigate the man's death and the suspicious monastery there. Apparently in 1945 an airplane carrying 'Germany's Greatest Treasure' made its final stop there, and the monks turn out quite different than perhaps Steed and his crew have anticipated...
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.
A strange message alerts Steed, Purdey, and Gambit to something strange going on. While Steed does his own research, Purdey and Gambit set out to help shed some light on the situation. However, the reality of the case is that due to a seventeen-year-old open case and a bout of amnesia, the legendary traitorous White Rat has at last begun to operate again. And Purdey is in imminent danger from her own romance.
In an attempt to break Steed's perfect shooting-range record, Purdey tackles the range with all her grace and skill. However, it's not enough as she misses one tiny percentage and gets hit with a mark. But other agents begin to die who have performed similarly, and Steed and Gambit start putting the clues together and find that they must work fast to save their friend and colleague before she succumbs to a nasty poison.
A bizarre series of deaths of high-ups in the government becomes the business of Steed and his colleagues when a personal friend of his becomes one of the deceased. However, due to suspicion from the delicate nature of the case...apparently people are being duplicated by an unscrupulous firm...Steed, Purdey, and Gambit all go off on their own and make individual progress into the case. However, it seems that the situation is too far-reaching and confusing for each alone. They must work together and figure out quickly, who's who and what's what, before they themselves become the next targets.
Released from prison after 9 years for spying, Burt Brandon heads straight for an abandoned well near Neverton containing unspecificed secret information. He is soon killed by 2 agents but has managed to post a package to his daughter. Steed recovers the package only to find it contains a pulp Western ""The Tale of the Big Why.""
Mason is the paymaster to a group of informants, but all is not what it seems: the informants are a single man. When Mason suspects this, he is murdered by Wallace, who has been lining his own pockets. Steed begins to investigate, and Wallace decides that the only option left is to frame Steed and kill him.
In 1965, a young Russian soldier guns down a Salvation Army Band and escapes only to fall down dead and grow old. In France, in 1977, a young Russian soldier attacks men wearing uniforms. Then a Russian unit is attacking an empty home. After one of the soldiers dies, he also ages. Why are the Russians attacking old targets and then aging? Steed and company are trying to find answers.
The Russian soldiers attacking in France were just the first wave. Two ""K"" agents are the true key to the plan. One ""K"" assassin is killed while assassinating a retired General. Who is the target for the second ""K"" agent and how might this start World War III? Only Steed, Gambit and Purdey can save the world.