Knowing the direct provenance of a piece can be thrilling. But jewels shrouded in secrecy can be even more ­enticing, as this Cartier bangle proves. Denoted simply as “property of a lady,” it’s signed and numbered, though shows only partial maker’s marks. Further mystery: Just one of the two pearls at the terminals could be tested (it was found to be natural and saltwater). “The bangle dates from the early 1920s,” says David Bennett, chairman of Sotheby’s Switzerland and of Sotheby’s Jewellery Division for Europe and the Middle East. “It’s fundamentally monochromatic, but also set with emeralds, diamonds, and two natural pearls. Altogether a very rare and probably one-of-a-kind item from one of the best periods of interwar Cartier design.” The piece sold at Sotheby’s Geneva for $802,428—proof that when it comes to great jewels, a little mystery goes a long way.