The Raw Shark Texts by Steven Hall

First things first, stay calm.

Eric Sanderson wakes up in a place he doesn't recognise, unable to remember who he is. All he has left are journal entries recalling Clio, a perfect love now gone. As he begins to piece his memories back together, Eric finds that he is being hunted by a creature that moves in language, that swims through the currents of human interaction.

With the help of his cynical cat Ian, Eric must search for the Ludovician, the force that is threatening his life, and Dr Trey Fidorus, the only man who knows the truth.