In 1943, the British secret services entrusted a particularly delicate mission to a French agent, Pierre Wagnies. This one, parachuted on the continent, must operate in the very heart of Paris of the occupation, in a palace where Germans and collaborators meet. There he found an old friend, Delancourt, a fencing champion like him, who replaced him with his wife Camille. Delancourt reveals to him that he is also participating in Operation "Judas". However, the sequence of events leads Wagnies to suppose that Delancourt would rather work for the Germans. At the same time, his passion for his ex-wife is reborn.