A man arrives in a Manhattan psychiatric unit, claiming to come from the planet K-PAX. Is he delusional, MPD and amnesiac, or telling the truth? His detailed, deadpan and sometimes literal answers to interrogation are often quite funny, though it is never clear whether this is deliberate on his part. He has great insight and empathy with animals and mental patients, great knowledge of astronomy, only eats fruit (skin and all), can see UV spectrum and can apparently disappear on a beam of light (using a mirror). Are these tricks, and if not, what is the explanation?
Similarities with One Flew Over the Cuckoo's Nest, the Man Who Mistook His Wife for a Hat and the film 12 Monkeys, but more ambiguous.
The sequels are not as good:
K Pax II: http://www.goodreads.com/review/show/24081161
K Pax III: http://www.goodreads.com/review/show/23324833