38. Tied up in Tinsel by Ngaio Marsh

ISBN 0 00 613215 4 - Fontana/Collins 1972
Hilary Bill-Tasman has hired staff for his English country mansion straight out of some of Britain's most notorious prisons - Wormwood Scrubs, Broadmoor and the (fictional?) Vale. Each man served time for a single murder/manslaughter and has adapted to a life in service to varying degrees. Superintendant Roderick Alleyn's wife Troy is at Halberd's Manor to paint Hilary's portrait over the Christmas Holiday and so is on the scene when Moult, visiting Colonel Forrester's much maligned manservant goes missing.
From answers.com: Marsh, Dame Ngaio (nī'ō) , 1899–1982, New Zealand detective story writer. She was an art student, actress, and theatrical producer before her first novel, A Man Lay Dead, was published in 1934. Her many mystery novels, acute in characterization and literate in style, reflect her knowledge of the art studio and the theater. They include Artists in Crime (1938), Died in the Wool (1945), False Scent (1959), Killer Dolphin (1966), Last Ditch (1978), Photo Finish (1980), and her last book, Light Thickens, published posthumously (1982). She was made a Dame of the British Empire in 1966.