Jewel thieves, murder, and a manhunt swirl around a sailor off a cargo ship in post-war London.

During the War, a British agent travels to the remote Glennye Castle in the wilds of Scotland to investigate a mysterious murder by a masked phantom. Who or what is the phantom? And how are the Germans involved?

It is the end of the 18th century and smuggling is considered to be a legitimate spare-time occupation for most fishermen around the British shores. But when a gang of cut-throats, led by the infamous Black John (Bernard Lee) begins to lure ships onto the rocks of Smugglers Bay, and murdering their crews for the sake of loot, the fishermen begin to fear for their livelihoods. In desperation, they appeal to the local magistrate Squire Trevenyan (Peter Cushing).