The Diabolical Masterminds of Series 4 (1965–6)

While Steed is on holidays on the continent, Mrs. Peel is abducted by a criminal gang led by Gregorio Auntie. He runs a business called “Art Incorporated” who make the bold promise of being able to get their customers anything - or anyone - they want, without limit, but the price will be high... The Russian agent Ivanoff has paid them to get him Mrs. Peel, we assume for his government to extract secrets from, although you can never be too sure given what she’s wearing when kidnapped. Steed returns and unmasks her replacement, then tracks down the villains and bids in their auction of Mrs. Peel when Ivanoff is arrested.
Recognised by Art Incorporated’s assassin, he overcomes the guards and frees the caged bird.

Doctor Adams is a top physicist for the government, who’s started acting suspiciously and playing a lot of golf. Why would he want to ruin a good walk? The ministry wants to find out, and send the Avengers to find out. The truth is, he’s passing secrets to the other side, using the daily passing of a Russian satellite over the golf course. Under the 13th green is a transmitting station complete with two-way television and tracking equipment. Behind it all is the seemingly blustering Colonel Watson, who controls the course through his thugs, Reed and Jackson.

Behind the Terpsichorean Dance Academy lurks an evil mastermind, the prong in the fork of enemy intelligence goading the side of England. The apparently drunken Chester Reed, orchestra leader at said establishment, is the controller of a gang of sleepers, who ingratiate themselves into society by replacing loners who join the school that resemble the sleepers they want to install.
It all goes a bit pear-shaped when Willi Fehr, a Politburo agent is nearly struck by a car while pushing a pram containing the body of one of the lonely dancers. In a flash Mrs. Peel is tripping the light fantastic and Steed is presenting himself as someone who won’t be missed.

The coup of the century - Dr. Long, a Ministry psychologist, has discovered many returned servicemen actually miss the rush of the battlefield, and are rampaging around the quiet English countryside seeking thrills. He sees a potential to harness this destructive energy - his own private army of fearless die-hards. After a bit of weeding of the chaff he unveils his grand plan - the theft of the Crown Jewels from the Tower of London. Never attempted before because the dangers were too great, for his band this would be an impetus. Once the jewels were his, he could command even greater plans, or at least that how his megalomania runs.
Step in the Avengers and his bands throw in their roses, their leader revealed to be a cowardly sneak before his death.