West Germany, 1954. Lance Bombardier Evans, a sheltered middle-class National Serviceman, is about to be sent back to England to undertake a second attempt at officer training. But first he has to get through one night of guard duty without incident. Evans is in charge of a section of six men detailed to guard an anti-aircraft Bofors gun at a British military base. It soon becomes clear that, with the exception of Gunner Flynn, none of the section have any respect for Evans, guessing rightly that he has no enthusiasm and little ability in his role. Gunner O'Rourke in particular is troublesome and insubordinate, his contempt for Evans spurring him to test the authority and patience of the weak-willed non-commissioned officer (NCO). Evans' fumbling attempts to engage him in friendly conversation only make matters worse. O'Rourke strikes one of the other men, Gunner Rowe, and then dares Evans to place him on a disciplinary charge, but the NCO is too nervously intimidated to do so. O'Rourke and his sidekick Gunner Featherstone insist on being allowed to go to the NAAFI to buy cigarettes and Evans ill-advisedly lets them go.
O'Rourke confides to Featherstone that at midnight it will be his 30th birthday and the two decide to go the canteen and start drinking, knowing full well it is forbidden whilst on guard duty. O'Rourke, having endured a grim childhood and the harsh, unjust punishments of the army for all his adult life, is at breaking point. Drunk and unstable, he tries to kill himself by jumping out of an upper-storey window but only suffers minor injuries. Evans refuses to report the incident but not out of any genuine concern for O'Rourke but rather out of fear that it might affect his chances of becoming an officer. Sgt Walker, a much stronger NCO, arrives on a visit only to find Evans has apparently lost control of his section. Walker, aware of Evans' lack of experience, is prepared to turn a blind eye to the mess provided Evans disciplines O'Rourke. An exasperated Flynn tries to convince Evans that he needs to exert some authority and that his attempts to win O'Rourke over by being lenient will not work.
O'Rourke and Featherstone, drunk and dishevelled, finally return. Ignoring Flynn's advice to report them, Evans is still convinced he can retrieve the situation himself and he puts O'Rourke on guard duty. Walker and Lt. Pickering arrive for the nightly inspection when Evans is checking on O'Rourke, still trying to talk him round. O'Rourke angrily accuses Evans of caring more about his own chances of becoming an officer than he does about the welfare of his own men. Evans admits that this is true, saying that becoming an officer represents his only chance of going home. O'Rourke threatens to attempt suicide again but Evans is too preoccupied with his own problems to really hear him. Walker orders the section to assemble for inspection and Evans goes back to the guard hut only to be ordered to fetch O'Rourke. He goes back to the Bofors gun only to discover that O'Rourke has stripped to the waist and fatally stabbed himself in the abdomen with a bayonet. Evans angrily kicks O'Rourke's corpse, knowing that his chances of going back to England are ruined. Walker and Lt Pickering arrive and Evans, now destined to spend the rest of his service in the ranks, has to face the full force of military punishment.
