The story is set during the opening months of World War II and it concerns a young pilot, Roderick 'Jerry' Chambers, who is part of an air patrol unit guarding the southern coast of England—around Portsmouth. One day, Chambers sees a submarine and, believing it to be German, attacks with his weaponry and bombs. The submarine is sunk. Back at the base, it is revealed that the sunken submarine was, in fact, a British vessel. Chambers escapes discipline but is censured and posted far away to the north of England. Meanwhile, by a curious chain of coincidences, his love-interest, Mona Stevens (a local barmaid), discovers that the submarine was, in truth, a German vessel—it having previously attacked and sunk the missing British sub that Chambers was accused of sinking. Chambers is offered a chance to redeem himself in a dangerous mission to test a new marine attack system. His plane explodes in mid-air but he survives, and manages to make his report.