Mortimer Cleveland, an authority in mental science, finds himself stranded in the bare Wiltshire downs in the driving rain after a second car tyre puncture within ten minutes of each other. He spots a light in the distance and makes his way to the house of the Dinsmead family. They invite him in, offering freshly made tea and viands. The family seem hospitable but Cleveland feels something is not right. Maggie seems afraid. The two daughters are both pretty but look nothing alike. The daughters are sent upstairs to prepare the room for Cleveland; when he retires he notices the table by his bed is smothered in dust. Written in the dust are three clearly visible letters “SOS”, confirming his suspicions.