A young teacher on her way to a position in Transylvania helps a young man escape the shackles his mother has put on him. In so doing she innocently unleashes the horrors of the undead once again on the populace, including those at her school for ladies. Luckily for some, Dr Van Helsing is already on his way.

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 chance discovery leads American mining engineer Ben Harris and acquaintance Harold to discover a lost city under the sea while searching for their kidnapped friend Jill. Held captive in the underwater city by the tyrannical Captain (Vincent Price), and his crew of former smugglers, the three plot to escape…