The Diabolical Masterminds of The New Avengers

A change encounter with a security staffer called Craig who is the spitting image of Terrison leads to the staffer’s death and Terrison taking his place. Five years later, he’s in Charge of a security department and his fellow ex-clochard Mullins is still killing anyone who crosses their paths - but they now have a grander scheme to replace all high placed security staff, and the prime minister himself, with doubles whom they control.
The plot is exposed when one double suddenly dies of a heart attack and Steed realises the corpse is not that of his friend.

Brady hears of the trial of a new nerve gas which causes everyone in the exposed area to pass out unless innoculated and steals the gas so that he and his gang can raid all the banks in the City of London on what must be the sleepiest Sunday afternoon in town ever.
He’d forgotten that the New Avengers lived in town, and had been innoculated though...

Juventor, known to the department as a dangerous mercenary, arrives in Britain with a brain-transfer machine stolen from a murdered professor - he offers it for sale to various enemy embassies and proves it works to one official by transferring knowledge of dancing from a tap dance to the official. He proposes the theft of the security information from the “Three Handed Game” - three civilians with photographic memories who have been given every third word of some top secret information. He succeeds in stealing the information, but the New Avengers catch up with him and dance him off stage.

Bored with Home Defence, Colonel Miller and his regiment of commandos hire themselves out as mercenaries on the world stage and finally decide they’ve done enough service as fighters and plan to steal the treasures of a Middle Eastern country, implicating Britian and retiring on the riches to a distant African principality.

Greedy research scientist Charles Thornton steals secrets from the goverment laboratory he’s working for to develop a ‘growth hormone’ based upon an unstable radioactive isotope. His hapless colleague Carter spills some of the fluid down a sink, resulting in the creation of a massive rat that starts killing people in London’s sewers.

Ten years earlier, Steed shot the defecting Mark Crayford - an old school chum - on the East German border and the grudge-harbouring Crayford, knowing himself to be dying from the bullet still lodged in his chest, arranges for himself to be listed as dead so he can return to Britain incognito and kill Steed in revenge.
He coerces a yough thug called Hara to help him, and systematically terrorises Steed, then kidnaps Purdey but dies before he can exact his revenge.

Departmental security officer Coldstream is a double agent, who coerces colleagues into visiting his health farm, where they are subjected to stress-condirioning. After the conditioning, the agents can be killed simply by exposure to objects that remind them of the conditioning programme.
He’s assisted at the farm by the psychologist Reresby, wh devised the programme, and a bevy of pretty young nurses who encourage the victims to persevere beyond the limits of their endurance.

Wallace, in Charge of the informers division, has been siphoning off funds in a scam whereby he pretended to be several different informers through the use of disguises. His fraud is discovered by paymaster - and frind Steed - Freddy, who is killed for his trouble, and Wallace tries to frame Steed for his and two other murders. He co-opts hitman Richards to do his dirty work but Steed’s cunning and Richards’ capture lead to his arrest.