18 - Diamond Pin by Carolyn Wells

Venture into the opulent world of eccentric New York widow Ursula Pell, infamous for her cruel pranks on her guests, especially her niece and nephew, the future inheritors of her vast gemstone fortune. When Ursula is discovered brutally murdered in a locked room after a dinner party, the suspicion first falls on her niece Iris, who recently fell prey to Ursulas humiliating jokes. However, as evidence surfaces, the spotlight shifts to her nephew. The location of Ursulas hidden gemstones and the promised diamond pin remains a mystery. Enter the renowned detective Fleming Stone, tasked with proving the nephews innocence, determining the true worth of the diamond pin, and unmasking Ursulas killer.