Warsaw 1938; Colonel Jean Francois Mercier (Tennant) is a French Military Attache in Warsaw. He is also a spy on a mission, which takes him undercover to Czechoslovakia, on the trail of the elusive ‘Chaika’, a man who can lead him into the heart of the Nazi war machine.
Meanwhile back in Warsaw, Anna Skarbek (Montgomery), his erstwhile mistress, is devastated by news of her ex-lover and political refugee and journalist Maxim Mostov. Heartbroken, she flees to Spain on a League of Nations mission of mercy.
As the Nazi storm clouds gather over Europe, dashing Polish Colonel Antoni Pakulski undertakes his own mission that goes to the heart of protecting the very future of Poland itself.