Second paragraph of Part 3:It was not the Other. He was thinner, and not quite so tall.
Clarke's first novel in the fifteen years since
Jonathan Strange & Mr Norrell, a much much shorter book, in which the eponymous protagonist is one of two living inhabitants of a vast building which seems to be the entire world. Gradually the truth about the narrator's past and about the world they are in becomes clear. Intense and intricate.
You can get it here.