At the French embassy in Warsaw, the new military attache, Colonel Jean-Francois Mercier (Tennant), is drawn into a world of abduction, betrayal and intrigue in the diplomatic salons and back alleys of the city. At the same time, the handsome aristocrat is involved in a passionate love affair with a Parisian woman of Polish heritage (Montgomery), a lawyer for the League of Nations. Risking his life, Mercier works in the shadows amid a remarkable cast of characters, some known to him as spies, some never to be revealed. It is a city where people drink and fight and spy and love, because no one knows what tomorrow will bring.