Corporal John Bramble [Franchot Tone] is the sole survivor of a British tank crew after Erwin Rommel [Erich von Stroheim] and his Afrika Korps overrun Tobruk in June 1942 and press the British back into Egypt. He stumbles into the vast North African desert and wanders into the small, sun-baked town of Sidi Halfaya, where he discovers the Empress of Britain, a quiet hotel run by Farid [Akim Tamiroff]. The only other employee is the French chambermaid Mouche [Anne Baxter], since the cook fled with the British and the waiter Davos was killed the night before by German bombing.
Farid hides the unconscious Bramble when the Germans swiftly seize the hotel to use it as their headquarters for Field Marshal Rommel’s staff. Bramble adopts the identity of Paul Davos [Franchot Tone] to save himself, slipping into a role of trust while the real Davos remains missing. When Rommel summons him for a private chat, Bramble is stunned to learn that Davos was a valued German spy, yet he manages to maintain the act. He is told that his assignment is to be sent to Cairo next.
Later, Bramble covertly pockets a pistol from the genial, music-loving Italian General Sebastiano [Fortunio Bonanova], intending to shoot Rommel and end the charade at dawn. Not wanting trouble, Mouche steals the pistol and waits on Rommel herself, a choice that will complicate the hotel’s delicate balance of loyalties. When several captured British officers arrive for a luncheon with Rommel, one of them recognizes that Davos has been replaced. Bramble privately explains who he is and what he plans to do, and Rommel’s guests are drawn into a dangerous game of deception and intelligence.
At the luncheon, Rommel teases his guests and invites them to ask twenty questions about his future plans, a moment Bramble watches with keen interest. Through the conversation and Rommel’s later remarks, Bramble deduces that the field marshal, who had posed as a benign archeologist before the war, secretly prepared five hidden supply dumps—known as the Five Graves to Cairo—to fuel a march across Egypt. The final clue appears when Bramble realizes Rommel’s cryptic references to points Y, P, and T correspond to the letters of the word “Egypt” printed on Rommel’s map.
Meanwhile, Bramble and Mouche clash over loyalties. She despises the British, convinced they abandoned the French, including her two brothers, at Dunkirk. He, in turn, is disgusted by how she courts the Germans. Yet her motives prove not to be mercenary: she pleads with Rommel to release her wounded soldier brother from a concentration camp. Rommel remains unmoved, but his aide Lieutenant Schwegler [Peter van Eyck] is more sympathetic and plays along, showing her fake telegrams to and from Germany.
That night, during an Allied air raid, Schwegler uncovers the body of the real Davos, exposed by the bombing. In the ensuing confusion, Bramble kills the German and hides the body in Mouche’s servants’ room. When Mouche discovers the truth, she threatens to reveal him, but she has a change of heart and protects him. Schwegler’s body is soon found, and Rommel accuses Mouche of murder after discovering he was lying about trying to secure her brother’s release. To protect Bramble, Mouche confirms the charge.
Bramble departs for Cairo, yet he arranges for Farid to present evidence the next day at Mouche’s trial that “Davos” committed the crime. Bramble’s intelligence enables the British to blow up the five dumps, thwarting Rommel’s strategic plan and setting the stage for the Second Battle of El Alamein. When Bramble returns to Sidi Halfaya in triumph with his unit, he learns that Mouche has been executed by the Germans, despite being exonerated at her trial, because she would not stop insisting that the British would return. Bramble takes the parasol he bought her in Cairo and places it above her grave, a quiet memorial to a woman who walked a perilous line between love, loyalty, and betrayal.
