Just returned from a nasty mission to Venice, Ian Heath is on hand to prevent the kidnapping of a young woman outside a theatre. Intrigued, he learns that she is the orphaned niece of a recluse inventor, heading to the man's remote Dartmoor manor called Doone Hall. Sir Harker Bellamy is interested for a different reason and send Heath to the region to learn if there is any truth to the fear that German spies were after the inventor's secrets. Heath will also have to deal with the fact that the house is said to be haunted by a real vampire.