Adam Blaney (Edward Brayshaw) and Bill Knight (Malcolm Reynolds) are performing some maintenance duties out on the Moon’s surface when Bill begins to have trouble breathing. Adam saves him and manages to get him back to base. It turns out that Bill’s oxygen tanks were empty. Bill believes he checked his tanks before he went out but now he is not sure.
Professor Kate Weyman (Anne Ridler) is working on the radio telescope when an explosion damages it. Kate was trying to boost a signal she was sending. She engaged an override to facilitate receiving a weak signal and then unengaged the override when her test was completed. However, when the equipment is examined, the override was still engaged. Repairs will take some time and will cost some money.
There seems to be a lot of accidents happening at the base. Director Caulder (Donald Houston) also has issues with budget cuts and time constraints. It appears that everyone is being pushed beyond their abilities. Deputy Director Lebrun (Ralph Bates) believes that Caulder is being too lenient with everyone. Moral is being affected. Adam Blaney seems to have an opinion about everything that has happened and why everyone is making mistakes. He has no trouble expressing his opinions to all. Adam was supposed to go on the first expedition to Venus, but a heart problem kept him off the crew. He spends a lot of time pretending not to whine about it.
Caulder has to look beyond the accidents and begins to believe that they may not be accidents but deliberate sabotage by someone having a nervous breakdown. His problem is discovering who, out of everyone on the base, is playing this psychological game of destruction.
The term Achilles' heel refers to a weakness, in spite of overall strength, that if exploited, can lead to downfall. The mythological origin of the term refers to a physical vulnerability but colloquially it also refers to any attribute or quality in a person that can lead to a collapse or breakdown.
At one time all six episodes of “Moonbase 3” were lost when the BBC threw out most of its archive sometime in the 1970s. Eventually copies were found at an American television station.