There’s a palpable sense of unease in this episode – right from the opening few minutes. Lisa visits Sophie (a key link in the escape line) to see if she will take three new evaders. Sophie – genial as ever – is only too happy to help, but Lisa can’t stay in the sanctuary of Sophie’s comfortable house for long. But when she leaves, the problems really begin ….

I think part of the reason why the stakes feel a little higher than usual (even before anything really bad happens) is that we don’t have a Candide scene until we’re about twenty minutes in. Usually, the sight of the Candide serves as a reassurance – no matter how bad things are outside, the Candide is a place where plans can be made and problems solved.

But with no Candide, the real world feels a little harsher. This is demonstrated by the sight of Natalie and two airmen (played by the very recognisable figures of Daniel Hill and John Alkin) sitting shivering on park benches the rain. During these scenes there’s a curious red herring – a woman pushing a pram (containing not a baby, but a doll) is rather conspicuous. Is she a member of the escape line or could she be a spy? Actually she turns out to have nothing to do with the story at all, so it’s odd the way the camera favours her (possibly this was a directorial flourish added by Viktors Ritelis).

Alkin would spend several years in court (Crown Court, that is) while Hill was only at the start of his career. He’d return to Secret Army with a much larger role in the season two story The Big One (and would also work again for Gerard Glasiter in the serials Blood Money and Skorpion). The Welsh accent he essays today came as a bit of a shock, but luckily he only had a handful of lines (boyo).

The first odd piece of plotting occurs after Lisa is arrested. Earlier, Lisa told Sophie that Natalie was on her way with the evaders. That’s fine, but according to Natalie they were waiting in the park for Lisa to lead them to Sophie’s house. That makes no sense – it’s quite clear that Natalie was familiar with Sophie, so why wait for Lisa? Indeed, having two key members of Lifeline in the same place seems to be a bit risky. 

I can see why, in story terms, it happened (Natalie has to be made aware that Lisa had been taken) but it’s just clumsily done. The fact that we never see the airmen again reinforces the point that they existed only to put Lisa into a part of France where she might get picked up.

Lisa visited Julius (Shaun Curry) – a member of the resistance who mughr have had news about Lifeline’s contacts in Paris. Curry and Jan Francis would go on to work together again in Just Good Friends but it’s fair to say that the taciturn Julius is a world away from the ebullient Les Pinner.

Lisa was unlucky enough to be in the wrong place at the wrong time. Juluis is arrested by the police and Lisa – simply by being there – is guilty by association. She’s interrogated on the spot by Inspector Landre (Gerald James). This was an excellent performance by James – all the more chilling for the fact that Landre remains so calm and matter of fact.

Lisa is sent to a local prison, pending further investigation. It’s the point of the story where you wish that the storyline had been eked out over several episodes as (good though it is) it now has to be concluded in double quick time. And we’ve not yet mentioned the quite substantial secondary plot of today’s episode.

Quickly befriended by her cellmates, Denise (Helen Gill) and Maria (Souad Faress), Lisa is able to prove her identity to the resistance leader, Jan (Damian Thomas), and therefore joins the others in a daring escape attempt. Hmm, okay. As I’ve said, it’s a shame that events now move so fast and it’s also hard to swallow the fact that for about half an hour every evening all the German guards go off for a bite to eat, leaving the prison so deserted that it’s possible just to walk out. Presumably there’s no guards outside, or searchlights, or dogs, or barbed wire. Not much of a prison then.

Still, Gill and Faress do sketch their characters very deftly even though they’re not given that much to work with, and the fact that Denise and Maria don’t escape (and face being shot) helps to rachet up the tension levels even more.

While all this is going on, Gaston finds himself a prisoner of Kessler. There’s excellent work from James Bree, Clifford Rose and Maria Charles during these scenes. If Lisa’s escape never really seems in doubt, then it seems equally clear that poor old Gaston is doomed. Small touches – Gaston’s unshaved face, red-rimmed eyes and askew tie – all help to demonstrate his inner turmoil, even though Bree resists the attempt to go over the top.

Maria Charles does indulge in histrionics, but then Louise (Charles) has just been told that her husband, Gaston, has been shot by the Gestapo, so that’s understandable. Viktors Ritelis throws in a slightly showy, but effective, shot towards the end of the episode. A distressed Maria, wandering the street at night, stops to paint a red V for Victory sign. As she collapses, dragging her hands through the paint, we intercut to Gaston’s death scene again (which eerily mimicked this moment).

If one were being picky (and I can’t help it) you’d have to say that it’s very convenient that Lisa suddenly appears to find her aunt prostate on the floor. It’s also not clear why Kessler – having decided that Gaston is part of the escape line – decides not to question any of his closest relatives (Louise, Lisa).

And finally, it seems slightly strange that nobody interrogates Lisa when she’s in prison or checks out her story. So that when she destroys her file in the prison office, it appears that all records of her arrest are removed and the story is over. That’s obviously not right, as we saw Inspector Landre writing in his notebook, but this is conveniently forgotten.

But minor quibbles apart, this is a top notch episode. Yes, Lisa’s escape can’t help but feel contrived, but it’s contrasted by Gaston’s self-sacrifice (deliberately running towards a guard in the hope he’d be killed before undergoing interrogation).