On sick leave from Scotland Yard, Inspector Alan Grant is planning a quiet holiday with an old school chum to recover from overwork and mental fatigue. Traveling on the night train to Scotland, however, Grant stumbles upon a dead man and a cryptic poem about "the stones that walk" and "the singing sand", which send him off on a fascinating search into the verse's meaning and the identity of the deceased. Despite his doctor's orders, Grant needs just this sort of casual inquiry to quiet his jangling nerves. But what begins as a leisurely pastime eventually turns into a full-blown investigation that leads Grant to discover not only the key to the poem but the truth about a most diabolical murder.