Paris, 1944.

Lieutenant Simon Riley, nicknamed the Ghost, is walking through the city some days after the liberation of Paris. Then, a scream. As a good honest man, he investigates. As he does so, a figure run past him, followed by an angry crowd. Helplessly, he watches as the young woman is hit, struck down, spit at, insulted. He asks the man next to him, and the man replies in broken English: "horizontal collaboration". That's when Simon steps in.