Steed and Emma walk around a deserted airfield for half an hour – making it my favourite episode (if it weren’t for The Grave-Diggers and Death at Bargain Prices). The first half is essentially a two-hander; unusually the only human in the pre-title card sequences is Steed himself (there’s also a canine who features more prominently – there are fabulous shots of her sprinter across fields of cows before running out in front of Steed’s bentley which he swerves into a tree.

Rather than responding to any kind of mystery or being assigned to some security detail, Steed is genuinely taking Mrs Peel to a party – to mark the closing of an airbase on which he used to serve. But instead of a party they find the airbase deserted, Marie Celeste style.

As every the dialogue and interplay between Steed and Mrs Peel is wonderful – more so for being centre stage here. Emma listens indulgently to Steed’s nostalgic wittering. Look at the way they walk – cool, casual, in step with one another. When things start to get strange, they need few words to know what to do – Emma just shouts out a rendezvous as they dash of in opposite directions to investigate.

Later, we get to see Steed rattled. He takes a drink. He throws it at the wall. It’s so uncharacteristic, and that’s what gives it the dramatic edge.

The atmosphere on the deserted airfield is fantastic – electrifyingly eerie. The sound of a milk float echoes around – such a clever, unexpected piece of sound design. (On the sound front, we also here ‘that’ gunshot/ricochet sound effect.)

The only weak point is the abrupt ending. The scheme is logical enough, but there scientific mumbo jumbo doesn’t quite convince, and some things are left unexplained (Why is Emma taken but Steed returned to the car? Why is the bicycle wheel still spinning the second time?) And the fight is a bit lame – but there’s laughing gas, so that is forgiven. And the diabolical mastermind is a dentist? Dentists in The Avengers is becoming a theme (see The Mauritius Penny and The Charmers).

Roy Kinnear is back for another, splendid appearance (after Esprit de Corps).

The bridge they cross on the way to the airfield is used several times in The Avengers – including in the title sequence of series 6 (it’s the one Tara runs along the balustrade of, just as Emma does here).

Tag scene transport: the milk float, of course.