Queen Elizabeth I (Flora Robson) is dealing with her country's deteriorating relationship with Spain. Michael Ingolby (Laurence Olivier), a naval officer whose father was killed fighting the Spanish, volunteers to go undercover in the Spanish court and learns plans are afoot to send an armada to ambush the British navy. Meanwhile, the aging Elizabeth, who has fallen for the dashing Ingolby, struggles with the fact that he is fixated on one of her beautiful ladies-in-waiting (Vivien Leigh).