When Professor Julius Arnell breathes his last in the British Museum Reading Room, it looks like death from natural causes. Who, after all, would have cause to murder a retired academic? Inspector Shelley's suspicions are aroused when he finds a packet of poisoned sugared almonds in the dead man's pocket; and a motive becomes clearer when he discovers Arnell's connection to a Texan oil millionaire. Soon another man plunges hundreds of feet into a reservoir on a Yorkshire moor. What can be the connection between two deaths? The mild-mannered museum visitor Henry Fairhurst adds his detective talents to Inspector Shelley's own, and together they set about solving one of the most baffling cases Shelley has ever encountered.