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.

A disgraced officer risks his life to help his childhood friends in battle.

A German submarine is sent to the Orkney Isles in 1917 to sink the British fleet.