This book is an excellent mystery surrounding the murder of Evelyn Hardcastle. The main protagonist is bound to solve her murder over the course of eight days by inhabiting "hosts" -- invitees of the gala being thrown in her honor.
Each day, he wakes up in the body of a different host, with different personality traits and quirks that he must navigate if he wants to solve the murder and escape the cycle. The only problem is that the longer he takes to solve it, the longer his enemies have to plot against him, some with violent intent.
With the help of Anna (whose name is the only part of his past he remembers), he must solve Evelyn's murder, evade the Footman, and rescue Anna before the end of his eighth day. But there is something even more ominous than a murder afoot in Blackheath.
This is one of the best mysteries I've read in a long time, on par with Agatha Christie. Superb plotting, great characters, AND science fiction? What more could you ask for?