We’re back in the world of the military – but this is far superior to The Golden Fleece. This time, the conspiracy is on a somewhat grander scale – an invasion – and the episode opens with a man being shot by firing squad. In the squad is Roy Kinnear (I only recently twigged that Rory is his son, despite the considerable resemblance). This is the first of his four appearances. Meanwhile John Thaw plays his only Avengers role.

There are terrific performances all round – it’s absolutely crucial that it’s played totally seriously, and it is – for though the plot is silly, like all the best Avengers story it has its own logic. There’s plenty of witty dialogue (and innuendo) for Steed and Cathy though…

“Anything you want to draw from stores?”

“Yes, but – I doubt if you’d issue it.”

Steed, going under cover as a Major, cannot work a washing machine any better than he can cook. And Cathy is apparently revealed to be heir to the throne of Scotland – we’re left wondering if this is true – right up to the brilliant brilliant denouement.

There’s an excellent last meal scene: Steed (having been sentenced to death by firing squad after a brief court martial) criticises the champagne.

I’m already through 8 episodes this month, so I’m certainly on track – but this is the kind of episode that makes me sad to think I will have watched them all by the end of the year. Perhaps I should make it an annual marathon. #Avenging2015 anyone?