Whilst attending to routine maintenance work on the Moon’s surface, Bill Knight (Malcolm Reynolds) nearly dies after he runs out of oxygen.  It seems incredible that he wouldn’t have checked he had a sufficient supply to last for the duration of his work-period, but it appears that he’s not alone in making basic errors.

Professor Kate Weyman (Anne Ridler) has to admit to Caulder that she must have left the cut-out disabled on a vital piece of equipment.  The resulting damage will cost both time and money to put right.

Caulder is aware that Moonbase 3 is like a functioning organism – everybody depends on everybody else.  And when efficiency starts to slip it could spell disaster for the whole base.  But what’s to be done?  Lebrun knows what he would do – enforce strict penalties for anybody who breaks the rules.  Caulder, on the other hand, doesn’t believe that such an inflexible policy would work – these people are scientists, he says, not children.

Eventually Dr Smith begins to wonder the accidents weren’t quite as accidental as they appear ……

Achilles Heel was the first of two scripts written by John Lucarotti.  It may not come as a complete surprise to learn that it’s probable the crisises were triggered by an unstable personality, but unlike the first two episodes it looks like it’s deliberate sabotage.

Adam Blaney (Edward Brayshaw) always seems to be about when problems occur – he was the one that rescued Bill Knight, for example – and all the evidence suggests he’s engineered these problems for his own ends.

He’s also able to wage a psychological war of nerves with some of the other Moonbase personnel, playing on their own fears and prejudices. So when talking to Lebrun, he casually mentions how lax he feels Caulder’s administration is – knowing full well that Lebrun will agree. It takes a while for Helen and Caulder to put all the pieces together and by the time they do, both Helen and Bill are placed in danger.

Why didn’t Dr Smith, who was the most qualified, identify that something was wrong with him?  Sadly, she’s taken in just like everybody else. Indeed even more so – she starts to become romantically attached to him.  This does seems rather inappropriate (like a doctor/patient relationship would be).

Edward Brayshaw enjoyed a lengthy career, but he’ll always be best known as the constantly perplexed Harold Meaker in Rentaghost.  He’s smoothly convincing as Adam, although it’s a difficult role – especially at the end, when Helen rejects his advances and his irrational side has to come to the fore.

The reason for his behaviour stems from his rejection as a pilot on a prestigious mission to Venus.  As he was denied the chance to end his career on a high, it appears he’s decided to ruin everybody else’s.  His actions suggest that he’s seriously unbalanced and the question must be how he was able to clear the physiological profiling which passed him fit for duty on the Moon.  But if the profiling had managed to weed out all the unstable characters there would have been very little drama in this series …

The opening minutes, with Bill Knight struggling on the Moon’s surface, is effectively shot – especially from his POV.  It’s just a pity that, impressive as the Moon surface is, once again we see the ground obviously move when anybody steps on it (a consequence of the way the set was built – presumably it would have been far too expensive to create a totally solid landscape).  But since all these scenes were prefilmed it’s surprising that they didn’t choose just to cut away from any especially unconvincing moments.

Although Helen is convinced that Adam was responsible for the sabotage, even if she doesn’t believe he was aware what he was doing, there’s no actual evidence to prove that both incidents weren’t genuine accidents. But his erratic behaviour provides Caulder with more than adequate grounds to ensure he’s returned to Earth.

Whilst Adam’s last-minute lurch into madness does feel a tad melodramatic, Achilles Heel is still a good story thanks to the guest performance of Brayshaw.