At one level this is a very good roman policier, set in Paris in the Belle Époque. It begins with a crime passionnel with what appears to be an obvious culprit, but Inspector Petit of the Sûreté soon suspects that there is more to it than meets the eye. The accused has meanwhile been whisked away to an asylum, not any asylum but the Salpêtrière, famous for its pioneering work on hysteria. Their patient is a very interesting case; he is blessed (or cursed) with total recall, he cannot forget anything.
The book soon moves to another level, opening up an exploration of the meaning of memory, consciousness, identity and guilt. Marcus Sedgwick is a prolific author of YA novels, which shows in his simple, direct language, fast pace and eventful plot. It does not deter him from opening up profound existential themes. A thriller that makes you think.