Dangerous Mourning — Anne Perry

No breath of scandal has ever touched the aristocratic Moidore family--until Sir Basil's beautiful widowed daughter is stabbed to death in her own bed, a shocking, incomprehensible tragedy.

Inspector William Monk is ordered to find her killer without delay--and in a manner that will give the least possible pain to the influential family. But Monk, brilliant and ambitious, is handicapped, both by lingering traces of amnesia and by the craven ineptitude of his supervisor, who would like nothing better than to see Monk fail.

With the intelligent help of Hester Latterly, a progressive young woman who served with Florence Nightingale in the Crimea, Monk gropes warily through the silence and shadows that obscure the case, knowing that with each step he comes closer to the appalling truth....