“Criminologist stages the theft of a picture to thwart his son's ambitions to be a detective.” - BFI.

The film is a historical drama set during the reign of Elizabeth I (Flora Robson), focusing on the English defeat of the Spanish Armada, whence the title. In 1588, relations between Spain and England are at the breaking point. With the support of Queen Elizabeth I, British sea raiders such as Sir Francis Drake regularly capture Spanish merchantmen bringing gold from the New World.

Scotland Yard sends a handwriting expert to a country house full of people with guilty secrets in order to solve a murder.