Man-Eater of Surrey Green - S4-E11
Revealing mistake: When Steed and Mrs Peel are fighting one another, the stunt doubles used bear absolutely no resemblance to the actors.
Factual error: The bad guys are supposedly auctioning off the stolen Mona Lisa. But they and their prospective buyers aren't very art savvy. The painting is more than twice the size of Da Vinci's actual masterpiece. (00:44:50)