The Face of a Stranger (William Monk Mystery, Book 1) - Anne Perry

He is not going to die, after all, in this Victorian pesthouse called a hospital. But the accident that felled him on a London street has left him with only half a life, because his memory and his entire past have vanished. His name, they tell him, is William Monk, and he is a London police detective; the mirror reflects a face that women woud like, but he senses he has been more feared than loved. Monk is given a particularly sensational case: the brutal murder of Major the Honourable Joscelin Grey, Crimean war hero and a popular man about town, in his rooms in fashionable Mecklenburgh Square. It's an assignment to make or break an investigator, for the exalted status of the victim puts any representative of the police in the precarious position of having to pry into a noble family's secrets. Suggesting that his superior, the wily Runcorn, hopes he will fail, Monk returns to a world where he cannot distinguish friend from foe. Grasping desperately for any clue to his own past and to the identity of the killer, each new revelation leads Monk step by terrifying step to the answers he seeks but dreads to find.