Steed and Mrs Peel must find out why an early warning radar is failing. Emma joins the staff of The Sir Horace Winslip Hospital for Ailing Railwaymen - while Steed has lunch with Sir Horace himself aboard his private, indoor train.
The Avengers investigate a series of murders of Corporate men, who have all been bidding on a new circuit element. Each one of them seems to have been killed by a powerful Karate blow, so Mrs. Peel visits a Karate Dojo, Steed's inquiries lead him to United Automation, where ex-Ministry scientist Dr. Armstrong is working on an electronic brain, not to mention cybernetic men.
When a colleague is found dead in a large London department store Steed and Mrs. Peel go undercover as staff members, exposing a dastardly plot by the wheelchair-bound Horatio Kane to devastate the capital with a huge bomb housed within the store.
When an agent in diving gear is found dead in a Scottish loch yet substantially taller than he was whilst he was alive Steed and Mrs. Peel visit a remote castle owned by the feuding De'ath cousins, Ian and Angus, to investigate the sinister goings-on.
Government minister Sir Clive Todd is wounded as he and other ministers try to steal top secret documents. He has no idea why he did it and hypnosis is suggested. All concerned belonged to a club for people with high I.Q.s called RANSACK, who are about to meet at a school. The Avengers join the club in order to expose the mastermind behind the next heist - the theft of a plane from an R.A.F. base.
On their way to a closing down party at an air base the Avengers' car crashes when they swerve to avoid hitting a dog. The air base proves to be deserted and Steed is knocked out. When he recovers he is back at the car but minus Mrs. Peel and the party, when he gets there, is in full swing. It would seem that he has gone back an hour in time.
A man-eating plant from outer space lands in Middle England and takes several top horticulturists as its prisoners in an effort to germinate the Earth. Fortunately for the Earth, Steed just happens to be a herbicidal maniac.
A mysterious Russian called Psev is arriving for a conference at which Steed and Mrs. Peel have been hired to act as the security guards. However, a man called Gordon Webster who is an exact double for Steed turns up and offers his services to Psev's entourage of four people, fooling Mrs. Peel in the process and agreeing to kill Steed. Though he is thwarted it turns out that Psev is also not exactly the man that everybody had expected him to be.
Steed has been having bad dreams involving Christmas trees and a man dressed as Santa Claus. At a party given by publisher and Dickens fan Brandon Storey, two telepathic spies attempt to read Steed's mind and make sense of the dream. However, the dream is echoed exactly by the events of the party, enabling Steed to spot the villains in advance and identify the dangerous Santa.
Dr. Wadkin, one of 7 scientist who have disappeared over the last year, suddenly reappears and attacks his Chinese wife. Steed and Peel find out that all of the missing scientist stayed at room 621 of the Chessman hotel before they vanished. Against her will, Emma poses as a receptionist while Steed pretends to be the famous food critic, M. Gourmet.
A man dressed in tropical clothes is found in Hertfortshire with an Kalayan arrow in his back. He has then fallen into a coma, yet there is no poison to be detected. All clues lead to an delusional Colonel living close by in a simulated tropical climate as if he were still serving in Kalaya. While Emma watches over an increasing number of comatose men, 'Major' Steed is invited into the Colonel's officers club with open arms, but is not allowed to leave.
When Steed returns home early from a holiday, he finds Mrs. Peel replaced by an actress, Georgie Price-Jones. Subsequently everyone involved in the hiring of Georgie is stabbed to death with double-O knitting needles. It seems the real Mrs. Peel has become Lot 17 of 'Art Incorporated', an organization which prides itself on being able to obtain any object for any one as long as the price is right.
Mrs. Peel is bequeathed an old house by an uncle Jack, whom she never knew existed. In the event, he did not exist. The house is a former lunatic asylum and it is all a ruse by a vengeful ex-employee of Mrs. Peel's to submit her to mind games which will drive her insane.
Economist James Broom is shot with an arrow by one of a group dressed as Robin Hood whilst on his way to meet a man opposed to his Utopian vision of a new Europe. The trail leads the Avengers to St. Bode's College, where anarchic students oppose traditional schools of thought. Could one of these have killed Broom? All is revealed at a fancy dress party where everyone is a character from the Robin Hood legend.
Eleven businessmen and counting have been mysteriously murdered, their affairs taken over by their able secretaries. The smell of perfume lingering over one of the dead bodies leads Mrs Peel to J.J. Hooter, who quickly becomes the next man to snuff it. With secretaries as their only clue, Steeds decides to hire one and Emma to take up the profession.
Two undercover agents are shot at Q.Q.F. Incorporated but one survives long enough to clue in Steed and Peel. So, Steed visits the Quite Quite Fantastic office (where fantasies are made to come true) while Emma looks into B. Bumble's honey shop. They soon surmise that someone is aiming for Prince Ali of Barabia, who is visiting London with his harem of 320 wives.