That old black magic

April 1943: four boys playing in Hagley Woods, Worcestershire make a gruesome discovery.

Inside an enormous elm tree, there is the body of a woman, her mouth stuffed with a length of cloth.

As the case goes cold, mysterious graffiti starts going up across the Midlands.

To Ross Spooner, a police officer working undercover for spiritualist magazine Two Worlds, the messages hold a sinister meaning.

He's been on the track of a German spy ring who have left a trail of black magic and mayhem across England, and this latest murder bears all the hallmarks of an ancient ritual.