Fleeing the humiliating arrest of her husband-to-be on the eve of their wedding, Celia Kilbride, a gems and jewellery expert, hopes to escape from public attention by lecturing on a brand-new cruise ship, the Queen Charlotte.

On board she meets eighty-six-year-old Lady Emily Haywood – the owner of a priceless emerald necklace that she intends to leave to a museum after the cruise. But three days out to sea Lady Emily is found dead with the necklace missing. And the list of suspects is large and growing.

Celia sets out to find the killer, not realizing that she has put herself in mortal danger before the ship reaches its final destination.