Wealthy New York widow Ursula Pell enjoys hosting parties and playing cruel jokes on her guests. If anyone complains about the humiliating mistreatment, she threatens to cut them out of her will. When Ursula's dead body is discovered in a locked-room the morning after a dinner party, suspicion initially points to the murder victim's niece Iris, the most recent recipient of one of Ursula's humiliating pranks. But there are many others competing for Ursula Pell's fortune in gems, which the eccentric widow hid somewhere and which includes a highly prized diamond pin. Who killed Ursula and how? And where is the stash of gemstones?