I bought a half dozen or so books in the SF Masterworks series the other day, and am about half way through the set now that I have a little time off. I just finished "The Fifth Head of Cerberus" by Gene Wolf.
The book is composed of three long stories involving the same pair of planets, which were colonized by Earth men, but which may or may not still be inhabited by their aboriginal people, who can change shape, and who may in fact be perfectly emulating and entirely replacing Earth men.
The third story in particular is an amazing narrative, cutting back and forth in time, seamlessly moving between diaries, third person narration, and transcripts of dialogues. The narrator of the third story sits in prison, and (shades of Kafka), his captors refuse to even tell him what he is accused of, because telling him would be a kind of admission that he might not already know what he had done, that he might actually be innocent. The dialogue is wonderfully executed, the interrogations remind me of the verbal thrust and parry of "Eternal Curse on the Reader of these Pages".
I suspect I'll need to reread the work at least once to start making sense of some of the subtleties. It's a brilliant and challenging work, and is highly recommended.