In the Spring of 1917, a Royal Flying Corps squadron is having more than its fair share of action on the Western Front. There is trouble within the squadron however, as spare parts and valuables have mysteriously disappeared, with no clue as to who is responsible. The squadron's commanding officer is worried that if it gets out there's a thief in their midst, it will adversely affect the morale of the men. When a senior officer apparently commits suicide, with his death linked to one of the thefts, the major knows that the time has come to solve the crimes quickly and discretely. To do this, he enlists the help of one of his senior pilots who was a detective before the war, charging him with the responsibility of investigating the death as well as the thefts. What appears to be an open-and-shut case quickly develops into something more sinister, leading the ex-detective to the realisation that there is more to the crimes than meets the eye. But how can he prove what his instinct tells him to be the truth?