One Summer night in 1914, Marjorie Beeston is startled by a masked intruder in her bedroom. She is even more startled when she discovers that the intruder is none other than Ronnie Randwall, a friend of her brother's. Ronnie is the proud inventor of a new kind of aeroplane, housed in a secret hangar on the nearby Bareacre Common - an installation so clandestine that the locals have taken to referring to its presence as the 'Mystery of the Common'. But the government base is not the only mystery to found in the locality of Bareacre Common. As the Great War looms on the horizon, what secret work took Ronnie to Marjorie's bedroom at Decoy Manor? And what has it to do with Marjorie and her family?

Originally published in 1920, this vintage thriller is set against the background of the outbreak of the First World War.