Near the end of World War II, American Major Falconer (Lancaster, Academy Award® - winning Best Actor ELMER GANTRY, 1960) leads his weary eight-man squadron to a perfectly preserved medieval castle in the Ardennes Forest. CASTLE KEEP's owner, the aging Count of Maldorais (Jean-Pierre Aumont), shelters the servicemen in hopes they will defend his fortress and his priceless collection of art masterpieces from the advancing German troops. But the servicemen have plans of their own. Major Falconer begins an illicit affair with the Count's beautiful young wife, while Sgt. Rossi (Falk) romances the wife of an absent baker. As the German soldiers push forward, a deadly game of possession ensues, leading to a spectacular ground battle for keeper of the castle.