As a token of his esteem for Captain George Cooper's prospective father-in-law, Lord Peters, the Rajah of Palakotta presents the captain with a casket of precious jewels. Cooper writes to his fiancée, telling her of this gift he will give her on his return. The notorious cracksman, Clement Rocca, robs the mail-train and reads the letter. He determines to steal the casket. He goes to the English hotel where the colonel and his daughter are staying. He meets them. At the same hotel is detective Harry Derwent. His suspicions are stirred by the action of Rocca. A telegram from Captain Cooper tells the time that his father and himself will arrive. The colonel and his daughter accept Rocca's invitation to join him in a shooting trip on an island off the coast. On arriving at the island, the criminal, on a pretext, leaves his guests. He returns to the mainland, knowing when the tide rises the island will be completely submerged.
