During the Napoleonic Wars, retreating Spanish forces shove a powerful cannon off a cliff to prevent the French from stealing it. The British send Capt. Anthony Trumbull (Cary Grant) to help the Spanish recapture it. When he arrives in Spain, Trumbull finds the cannon secured by Spanish rebels. As Trumbull and the rebel leader Miguel (Frank Sinatra) struggle to transport the cumbersome cannon through the mountains, the British officer falls for beautiful Spaniard Juana (Sophia Loren).