The world's finest ruby was stolen from the bride of Prince Kassim's great-grandfather several generations ago in India by a marauding rajah. It's now several decades later and the British have conquered India, and one day the ruby shows up for sale by a wealthy London jeweler, Sir John Garnett. Garnett has his own problems--there have been a rash of thefts of his wife's jewels, and he hires a private detective named James Brett to investigate. An agent for the Russian czar expresses interest in buying the ruby, but he's actually a member of a gang that specializes in jewel thefts and steals the ruby, hiding it in a box of chocolates belonging to Garnett's wife. Unbeknownst to Garnett, the jewel thieves and even Garnett's wife, she is actually involved in the theft of her jewels. Complications ensue.