"Nobody's Ring" by Terence Faherty

From: The Shamus Game ed. Robert J. Randisi. Signet, 2000.

In 1951 Hollywood, P.I. Scott Elliott finds an ostentatious sapphire ring left in the bathroom during a dinner party. No one at the party claims the ring, so Elliott visits local jewelers until one identifies the ring as his handiwork and tells Elliott who ordered it.

Elliott calls the jeweler's client to give the ring back, and the client requests they meet at a more private location. Soon after Elliott arrives there, he finds the client shot dead and is brought in by the police. Faherty keeps this long short story moving with many more twists. Well worth a read.