Not much Mrs Peel in this - for most of the ep she's replaced by 'companion of the week' Georgie Price-Jones (Liz 'Carry On' Fraser). The real Peel has been stolen by Art Incorporated, an organisation run by so-called Gregorio Auntie (Alfred Burke, returning from The Mauritius Penny).
Steed and Georgie have to track her down, avoiding Mary Merrall's murderous, knitting-needle-wielding old lady. It sounds silly but the impression she makes is actually extremely sinister. There's also a highly macabre running gag about corpses falling out of cupboards. But to lighten things up a bit, we have a very funny scene where Georgie successfully fights off the old lady while reading instructions out of a self-defence book she happens to be leafing through - eventually escaping by whacking her over the head with it.
Bernard Cribbins appears as convenor of a knitting circle (!). This provides an opportunity for one of the 'lots of people being drilled in doing something in unison' scenes which have recurred since the later part of series 3.
Mrs Peel does eventually reappear, imprisoned in a giant birdcage. I did wonder exactly why Auntie did this, and how he got her to put the sexy costume on. His receptionist has been given the task of poking her with a stick to liven her up, which I found strangely exciting. Her reaction to this treatment is a kind of bored petulance which is very amusing.
Ultimately this is another piece of series 4 fluff, but it's good fluff.
Also seen: Sylvia 'Amelia Ducat' Coleridge as a non-evil old lady, David 'Number Two in Living In Harmony' Bauer as the intending purchaser of Mrs Peel, and Maurice 'Karlton in Dalek Master Plan' Browning.