The Intruder, Lady at her Toilet, Surprised by her Lover

By 1665 de Hooch had left Delft for Amsterdam, and his pictures changed with the address. In Delft he had painted brick courtyards and back doorways in plain daylight. Amsterdam was the richer city and its buyers wanted rooms that looked like their own, so the floors get marble, the fabrics get satin, and the light goes deeper and warmer.

This is one of those Amsterdam interiors. A woman at her dressing table is caught by a man coming through the door, and the whole situation turns on that doorway. Looking from one room through an opening into another was the device de Hooch worked out in Delft in the late 1650s, in the years when Vermeer was a few streets away doing something close to it.

It hangs at Apsley House by Hyde Park Corner, in the collection the first Duke of Wellington brought home from the Peninsular War.