As a ship carrying Special Force Six, the forty intrepid infantrymen assigned to disable the massive German machine gun on Normandy Beach in advance of the Allied Fleet, nears its target, John Wynter, the British commander in charge, confers on deck with Brad Parker, an American captain. While awaiting landing, John reflects back to 1942, a happier time in his life: In an English village, John visits his sweetheart, Valerie Russell, the daughter of Brigadier Russell, to say goodbye before embarking upon a secret mission to Cairo. Before parting, they exchange pledges of everlasting love. As John's thoughts return to the present, Brad reflects on his arrival in Britain three years earlier: After suffering a broken leg in a parachute accident, Brad is discharged from the Air Force and assigned to limited service. Brad leaves his wife Janey behind in the States, and is sent to serve in Great Britain under the command of Col. Alexander Timmer. During their first meeting, Timmer sternly warns Brad about breaching security. Meanwhile, in the village, Val's father chastises several rowdy American soldiers about their lack of respect. Brad and Maj. Mills are then sent to apologize to the brigadier for the men's behavior. When Russell bristles and suggests that the entire village be put off limits to the boorish Americans, Brad becomes incensed and reminds Russell that the Americans are willing to sacrifice their lives in defense of Britain. After Brad and Mills leave, Val runs after them and apologizes for her father's behavior. Val explains that the British are a proud people who have never had to ask for help and therefore resent the intrusion of the Americans. Brad and Val meet again on a train bound for London, where Val is to work at the Red Cross Club. While sitting together, Brad tells Val about Janey and Val speaks of her absent soldier sweetheart. Because they are both lonely, Brad invites Val to dinner and she gladly accepts. As their relationship develops, Val encourages Brad to talk about his wife because it makes her feel "safe." One day, Val reads that eight officers have been killed in a desert raid, and fearing that John may be one of them, begins to feel guilty. When Val confides to Brad that she is falling in love with him, they decide to stop seeing each other, but Brad discovers that he is unable to stay away and they resume their affair. Timmer, determined to best his rival, Lt. Col. Cantrell, for a promotion, decides to join the invasion of a German stronghold in Dieppe, France, and orders Brad to accompany him as an observer. Timmer returns from the raid somber and shaken, one of the few survivors. On the road back to London, Timmer stops at a pub for a drink and boasts that he was at Dieppe. A reporter overhears him and prints the story in a newspaper, and Timmer is accused of violating an Allied prohibition against speaking to the press. Upon reaching London, Brad races into Val's arms. Soon after, Timmer's rival is promoted and Timmer's unit dispersed. When Brad learns that he is to leave immediately for Algiers, he tries to notify Val, but she has just left London to arrange for her father's funeral. The brigadier, depressed about his inability to serve his country, has committed suicide. Ten months pass, and Brad learns that his only chance of returning to London is to get assigned to Special Force Six, a perilous mission headed by Timmer. Ten days before he is to report for duty, Brad and Val joyously reunite and Brad informs Val that his wife has discovered their affair. Six days later, John, weak and wounded, arrives in London and goes to the Red Cross Club in search of Val. Overhearing that Val has a boyfriend, John hastily departs to wander the London streets. When a woman from the club notifies Val that John is looking for her, she bids Brad goodbye and goes to find John. Brad, meanwhile, proves himself physically fit for combat and is welcomed to Special Force Six by Timmer. Before leaving on the mission, Brad seeks out Val at the Red Cross Club. When Brad vows never to give her up, Val responds that she is devoted to John, who has regained his health. Soon after, Timmer suffers a nervous breakdown and is arrested for divulging secret plans before a crowd of strangers. Brad finally meets his rival when John is made the new mission commander. Brad's thoughts return to the present as the troops prepare to storm the beach. In the assault, Brad is seriously wounded, but the mission is successful. As Brad, confined to a stretcher, awaits his transport back to England, John praises him and wishes him good luck. After Brad is carried away, John pensively strolls along the beach and is killed by a landmine. In an English hospital, Brad, unaware of John's demise, sends a message to Val that he and John have survived. Val, who has been informed of John's death, receives the message and visits Brad, who is to be shipped home. From his hospital bed, Brad tells Val that he is reconciled to returning to Janey. Withholding news of John's fate, Val kisses Brad goodbye and walks away, alone.