In December 1941, New York bookmaker Steve Boland is more interested in drinking champagne with his beautiful neighbor Ruby than listening to news reports about the Japanese attack on Pearl Harbor. After being turned in to the police by his unhappy customers, whom he has been cheating, Steve is convicted for racketeering, but avoids a prison sentence by promising to enlist in the U.S. Army. Though he has no intention of serving his country, Steve is personally escorted to the recruiting office by the arresting officer. After only a few weeks of basic training, Steve has caused so much trouble that a military chaplain is called in to counsel him. Despite his lack of dedication, Steve is shipped out with the rest of his unit to England, but spends most of the ocean voyage under arrest, having been caught running a craps game. While on leave in London, Steve continues his crooked ways by working in the black market, hiding his loot in hollowed-out library books. Back with his unit, Steve spends most of his time on punishment duty, digging latrines, and is considered a coward by some of his fellow soldiers. Despite his best efforts to be dishonorably discharged, Steve remains in the Army and ends up fighting on the beaches of Normandy during the D-Day invasion, as well as marching into Paris when that city is liberated by the Allied forces. Steve and his unit soon become part of the invasion of Germany. While serving in the occupation force of a German town, Steve befriends Ilsa, a young woman he catches stealing food. Though she accepts his food and gifts, Ilsa initially rejects Steve's sexual advances, informing him that she is a virgin, but after he calls her a "cheat" for leading him on, she offers herself to him. For the first time in his life, however, Steve feels pangs of love and rejects her submission. When the Germans begin bombing the town in the middle of the night, Steve rushes back to Ilsa and admits his true feelings, which she returns in full. Unknown to both of them, Ilsa's brother Karl is part of an elite troop of German soldiers, known as "werewolves," who have been sent behind the front lines to commit acts of sabotage and murder against the Allied forces. Karl and his childhood friend Ludwig soon appear at Ilsa's door, disguised as American soldiers as part of a plan to destroy Allied morale by assassinating Gen. Dwight D. Eisenhower. When Ilsa tells them the war is already lost and that their assignment would only prolong it, Karl warns his sister that he would not hesitate to kill her if she did anything to jeopardize his mission. Meanwhile, Steve has been arrested for breaking curfew, but is so desperate to see Ilsa again that he escapes the stockade and goes AWOL. He arrives at her door just as Karl and Ludwig are leaving and immediately assumes the worse. Desperate to save her brother's life, Ilsa tells Steve all about Karl's mission and begs him to take her to his commanding officer. Brought before two Army Intelligence officers, Ilsa tells them everything she knows about Karl's detachment, noting that the "werewolves" were founded by Heinrich Himmler in 1943 and that their secret training ground was located in Poland. Having no luck in finding Karl and his men, Capt. Melton asks Ilsa to help them search the nearby forest for her brother, but she agrees to go only if Steve is brought along. Instead of finding Karl and his men, however, they are captured by the Germans, who are in the midst of preparing to ambush Eisenhower, who, they have discovered, through an intercepted military courier, is headed their way. In order to warn the Allied chief of staff, Ilsa breaks free from her captors, only to be shot in the back by one of Karl's men. During the ensuing firefight, Steve stabs Karl, then shoots Ludwig. The remaining "werewolves" are soon captured by Allied troops, and Steve carries the wounded Ilsa into the forest, assuring her that everything is "going to be all right."