Discovering the cause of the ghastly, shrieking sound, labeled the 'wailing witch', Hop felt certain that by questioning Roy Saunders, forcing him to divulge his contact in the underground aircraft plant, he could solve the puzzling mystery, and learn why four of the experimental models of Simon Gore's Flying Wing had been sabotaged. Feigning injury, Hop is lying in bed in the plant dispensary, from where he's been sending Major McColl on several mysterious errands...