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.

2 scientists are developing a new growth drug which could end world famine. Unfortunately some of the drug has been flushed down the sink resulting in something nasty in the sewers.

When Steed has a hoard of screaming teenagers rescue his intended victim, spymaster Perov seemingly commits suicide. But days later his system of sleeper agents, the House of Cards, activates, and Steed, Purdy & Gambit find themselves fighting trusted friends.

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.

The warning of a dying man tips Steed off that ecologist Rydercroft is to be killed at noon. All plans are taken to protect the man's aircraft but it still crashes. Soon the Avengers come up against a new breed of enemy.

The terrific trio come up against Professor Turner, a scientist with a lust for gold, and his protege Midas, whose touch is deadly.

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.

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.""

The trio are on the trail of a mysterious agent ""The Fox."" Although he escapes, he leaves a palm print on the roof of a car owned by the aged Miss Daly and the Avengers must preserve the print to make a positive ID on their target.

When the Avengers foil a drug drop arranged by a Chinese overlord, they find themselves on the run from his men, the Oriental being determined to have their heads on plates.

KGB agent Karl Sminsky is recruiting criminals to train as supremely skilled fighters in order to smash Canada's security system. The Avengers find themselves up against a team of supermen.

An old flame of Purdey's reappears when a missile goes missing from an air display. But what's the connection between that, a visiting Arab envoy, and a spy satellite photographing Buckinghamshire?

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.

Steed's plan to have 3 memory experts memorise a third of each of the Allied defence plans for courier purposes seems to have been a perfect success until Juvenator arrives with a machine capable of draining minds.

Agent X41 (codename ""Scapina"") is the USSR's most effective spy. But a photograph has fallen into the hands of the Avengers which may give a clue to his identity. The trail leads the trio to Toronto.

Paris: Steed captures his nemesis, the Unicorn. But when the Unicorn is accidentally killed by his own men, Steed must use all his cunning to avoid open warfare.