When Private Walker gets his call-up papers to join the regular army it comes as a shock to the platoon because he is useful to them for his black market activities. Wilson is chairing a committee and tries to get him turned down whilst Jones has him jumping off a ladder barefoot to induce flat feet. Ultimately he does get turned down because he is allergic to corned beef.

Captain Mainwaring is told that he can promote one of the privates in the platoon to lance-corporal and he chooses Frazer as being the most efficient. Unfortunately this leads to a bitter rivalry between Frazer - who keeps dishing out charge sheets and becomes unpopular - and Jones, culminating in a fight between the pair of them, and ultimately Mainwaring has to return Frazer to the ranks.

Whilst on fire-watching duty the platoon see a man shining a torch. He speaks with a European accent and has a dog called Fritz and they arrest him as an enemy agent. However, the man - Sigmund Murphy - tells them that he is a British subject and even helps them put out a fire in the church hall, after which Hodges explains that Sigmund is indeed a British citizen and the husband of his Auntie Ethel.