Captain Hastings and Poirot, in need of change of air, travel to Brighton. They stop at the Grand Metropolitan hotel, where they meet Mr and Mrs Opalsen. Mr. Opalsen is a rich stockbroker who amassed a fortune in the oil boom, and his wife collects jewellery using the proceeds. She is eager to show one of her famous necklaces, but when she goes to fetch it, discovers that her most precious asset has been stolen. Poirot is asked to assist.