Fleeing a disastrous and humiliating arrest of her husband-to-be on the eve of their wedding, Celia Kilbride, a gems and jewelry expert, hopes to escape from public attention by lecturing on a brand-new cruise ship. On board she meets eighty-six-year-old Lady Emily Haywood, 'Lady Em, ' as she is known throughout the world. Immensely wealthy, Lady Em is the owner of a priceless emerald necklace that she intends to leave to the Smithsonian after the cruise. Three days out to sea Lady Em is found dead. And the necklace is missing.