Case of the Disappearing Gauguin

A globetrotting Gold Rush heiress. An awkward Paris schoolmaster. A celebrated French actor. And a museum of history and art in California’s Central Valley. What do they have in common? They are all connected by an oil painting, a still life called Flowers and Fruit, that may or may not have been painted by the post-Impressionist Paul Gauguin.

In the decade that museums began to collect modern art,...