They dismissed the Mary Deare as a piece of leaking ironmongery taken off the junk heap. For forty years, this 6,000-ton freighter had tramped the seas, suffered shipwreck twice and been torpedoed three times in two world wars. Then one March night, battered and bruised,  she steamed out of the fog of the English Channel, her lights ablaze and her bridge deserted. Cabins that had been lived in recently were empty; food lay ready on the mess table – and of the crew, not a sign. Where were the crew? And what secret did she carry in her hold?