The Raw Shark Texts by Steven Hall

Eric Sanderson regains consciousness and breathing upon the carpet of a room he does not recognise and, on further probing within himself, without any memories whatsoever. A letter instructs him how to get to a Dr Randall who informs him that since he was traumatised by the death of his girlfriend Clio four years earlier he has suffered complete loss of memory, and that this is his 11th occurence. A room in his house is locked. Dr Randall warns him not to read the post that arrives through his door but eventually the Bluebeard moment occurs and Eric gives into the urge. He and us are then pitched into a world where the boundaries shift and Eric is pursued by a Ludovician shark, a conceptual predator that feeds on his memories and is determined to swallow him whole. Deeply moving, confusing, and very very intelligent