Major Brandt’s wife, Erika (Brigitte Kahn), is in Brussels for a brief visit. Their interactions later provide the spur which kicks the plot into gear, but before that there’s plenty of nice character development on offer.

Brandt is clearly delighted to see her (something she reciprocates, although in a rather cooler way). This is partially explained by the fact that, as a General’s daughter, she suffers from something of a superiority complex – for example, she has no wish to meet Kessler. A member of the SS is plainly a much lower form of life.

Plot-threads which pay off later in the year are established here. Erika now finds living in Berlin, which is suffering heavy bombing raids on a regular basis, intolerable. Fearful for her own life (and that of their children) she begs Brandt to move them to Brussels. This he declines to do, although he concedes that they should leave the city.

There’s an intriguing moment when she finds a photograph of an attractive young woman in his wardrobe. His mistress? Since we know that he’s a workaholic it would seem not and his protestations of innocence do appear to be sincere. And yet ….

You have to say that his explanation for its presence (the cleaning woman could have left it there) is a bit feeble.

Brandt has already tried and failed several times to infiltrate the escape line with one of his officers. Indeed, during series one it seemed like he was doing it every other week.

He hasn’t attempted it for a while, so I suppose it was bound to happen again. The way that the audience (and Lifeline) learn about it today is a touch contrived though. Brandt and Erika are having an argument in bed and he tells her the whole story (an infiltrator – accepted as genuine by London – will shortly be going down the line). But at that precise moment his cleaning lady happens to overhear the whole thing.

That’s hard to swallow moment number one. Hard to swallow moment number two is the fact she knows that Albert is the person who needs to be told about this straight away. Slightly clumsy plotting then.

Hans Van Broecken (Gunner Moller), Natalie’s uncle (and no friend of Albert), returns. As a German himself, he’s the ideal man to try and identify the spy, but given his loathing for Albert, will he agree? Yes of course, otherwise the plot would have floundered somewhat.

If he’s unsuccessful then there will be some difficult decisions to be made. With nineteen British airman in Brussels, one way out would be to shoot them all. It seems cold-blooded, but it might be necessary in order to protect the line.

Some familiar faces can be found amongst the motley collection of airmen. James Wynn (later to play Sooty Sutcliffe in Grange Hill) is one whilst Harry Fielder (someone with a list of credits longer than several arms) is another. The spy isn’t either of these though – but he’s eventually dealt with by Max, with a horrified Hans looking on.

Hans’ disgust that Max resorts to murder is a little difficult to credit. Did he think they’d just let him walk away? He might not have discovered too much about the escape route, but he still would have been able to identify a number of people (Max and Hans, for two).

As touched upon eadlier, the plotting of the episode feels a little suspect in places. We’re told several times that various airmen have been cleared of suspicion, but it’s not explained how this is done. Considering that the infiltrator appears to be, until the very last minute, a perfectly normal British officer it’s hard to work this out.

Kessler only features briefly, but his scene – a meal with Madeleine (Hazel McBride) – is still a fascinating one. There’s some light shone onto Kessler the private man (he admits to being lonely at times, which is why he’s sought the company of Madeline – he’s decided she’s a kindred spirit). And he almost (but not quite) declares that Brandt is his friend, explaining to Madeline that normally he’d be irritated by the superior attitude of Erika, but given his respect for Brandt he’s content not to make a scene.