In 1588, relations between Spain and England are at the breaking point. British sea raiders regularly capture Spanish merchantmen bringing gold from the New World with the support of Queen Elizabeth I. After a plot to depose her is discovered, she enlists Michael Ingolby, whose father was killed by the Inquisition, to go undercover and infiltrate the court of Philip of Spain. Masquerading as one of the traitors, Ingolby finds the names of British subjects in Spanish pay. He identifies the would-be assassins and discovers their plans to send the Armada against England. His feats earn Ingolby the love of a Spanish noblewoman, an English courtesan, and Queen Elizabeth herself as he takes the British fleet into battle. At the climax he leads a night attack on the Armada ships massed off the coast of England.