The Face of a Stranger — Anne Perry

His name, they tell him, is William Monk, and he is a London police detective. But the accident that felled him has left him with only half a life: his memory and his entire past have vanished.

Trying as best he can to hide that fact, Monk returns to work and finds himself assigned to the brutal murder of Major the Honorable Joscelin Grey, Crimean war hero and popular man about town, in his rooms in fashionable Mecklenburg Square.

Slowly the darkness begins to lighten as each new revelation leads Monk step by terrifying step to the answers he seeks but dreads to find....