A pirate ship, the Diablo, commanded by Robeles (Christopher Lee) takes part in the Spanish Armada but is badly damaged during the battle. Robeles takes his ship into the English marshes for repairs.
They then run into trouble when they find a small remote village. As the villagers don't know the Armada was defeated the pirates try to bluff their way to make the villagers think Spain now rules England.
It's all rollicking and swashbuckling good fun. Christopher Lee is excellent as the brutal pirate captain, Ernest Clark also plays a good role as the oily local aristocrat who is overly keen to ingratiate himself with the Spanish. John Cairney is the hero who refuses to bow down to the invaders.
The most impressive thing about the film though is the Diablo itself, a full-size galleon built for the film. Unfortunately it was not built very well and capsized leaving most of the cast and crew in the water!