Serving in the trenches of France during the First World War, battlefield nurse Bess Crawford is sent back to England in the early summer of 1917 with a convoy of severely burned men. One of her patients, a young pilot, has clung to a photograph of his wife ever since his plane went down, and Bess sees the photo every time she tends to him. After the patients are transferred to a clinic in Hampshire, Bess is given 48 hours of leave and plans to return to her flat in London to catch up on some much-needed sleep. But at the railway station there, in a mob of troops leaving for the front, Bess catches a glimpse of a familiar face-that of the same pilot's wife. She is bidding a very emotional farewell to a soldier.
Back in France days later, Bess picks up an old newspaper with a line drawing of the woman's face on the front page, and a plea from Scotland Yard asking if anyone has seen her. The woman had been murdered the very day Bess saw her at the terminal. Bess asks for leave to go to Scotland Yard to report what she knows. And thus she embarks on the search for a devious and very dangerous killer-a search that will put her own life in jeopardy.