In 1942 Casablanca during WWII, Max Vatan (Brad Pitt), a French-Canadian intelligence officer, meets French Resistance fighter Marianne Beausejour (Marion Cotillard), on a deadly mission behind enemy lines.

They fall in love while working together on a mission to kill a German official, and afterwards Max convinces Marianne to come with him to London to marry him. She does and the happy couple soon have a child together. However, their relationship is threatened by the pressures of war, especially when Max is told that Marianne may be a Nazi spy. He's given 72 hours to find out the truth, and if the suspicions are true, he's ordered to execute her or be hanged himself.