Locked-Room: The Double Turn by Carol Carnac (1956)

Adrian Delafield, once a great-in-demand painter of the Victorian era, now lives a secluded life at Firenze at St. John's Wood, looked after by his devoted maid, Miss Trimming. Trimming who is a religious fanatic keeps him away from 'the evils of the world'; one of those evils apparently being Delafield's own daughter, Virgilia Delafield, …