The quickest way to make an art detective stalk off in disgust is to mention The Thomas Crown Affair. Everything about the film infuriates the pros. Thieves aren’t slim figures in tuxedos; they’re brutes. They’re not connoisseurs who moon over stolen masterpieces behind locked doors but thugs who probably have never ventured into a museum except to rob it. But, inevitably, when great paintings disappear, some of the lustre of the artwork spills onto the thieves themselves. This gilt by association is almost entirely undeserved.

In July 1994, thieves made off with two Turners worth a total of £24 million, which were on loan from the Tate to a gallery in Germany. Sordid and simple, the real-life case had scarcely a hint of Hollywood glamour. The theft was a ‘stay behind’: the crooks