The boys put on an evening of patriotic songs to impress entertainments officer Hopkirk but the audience is full of Scotsmen who are disgusted and start a riot. Things look bleak for the company until the very effeminate new entertainments officer Fawcett arrives and loves the 'nice boys', as well as Ashwood's Noel Coward impersonation.
Colonel Bridges and two other medical officers come to the camp, looking for guinea pigs on whom to test a new anti-malaria serum. As they are a concert party the boys are expendable and therefore ideal. Williams bribes the men into having their shots by promising them beer but there are strange side effects as most of the company end up with swollen faces and Ashwood's hair starts to fall out. Williams exhibits signs of malaria but Bridges thinks it is psychosomatic and plans to shock him out of it by firing a gun. Instead he shoots himself in the foot.
The men are amused to learn that Williams had an affair with a titled married woman. Ashwood is disgusted but he has further problems when a female welfare officer, Captain Tollemache, takes a shine to him, marooning them both in the jungle when their jeep 'accidentally' runs out of petrol. The men answer his distress call and take petrol out to him but Lofty spills some, Williams throws down a dog end and a fire is started. After the men put out the fire they find the two captains asleep in a tree.
The BBC are recording a show from the camp. The men want to sing and Ashwood wants to put on his comedy revue 'Jungle Japes' but the producer wants it to be a request show. Mrs Parkin has asked for 'I'll Be Seeing You' to be played for her boy. They hear a message from her in which she mentions Willams, as he is often referred to in her son's letters home. Williams is surer than ever that he and Mrs Parkin are the parents of the young gunner. As a result Gloria hides the record and the group sings live.
In an effort to get rid of him, the men persuade Williams to apply for a new fast track process promoting sergeant majors to lieutenants. The Colonel and the Captain fear he is too common and put him to the test by giving him dinner with the Brigadier. However a series of mishaps and the fact that the Brigadier also rose from the ranks leads to his approving Williams' bid for promotion. But the war only has months to go and Williams does not want to waste them at officer training camp so he withdraws his application.
The Japanese are retreating and the Colonel is keen for the company to become an assault team, entertaining troops at the front line, so he sends them on a battle course with Ashwood. Unfortunately they get lost though they find and activate some homing devices, which lead to their being bombed by British planes who mistake them for Japanese. To identify themselves they write 'British' in the sand and get Lofty to take his clothes off. Fortunately the only casualty is the ventriloquist's dummy.