Algis Budrys 
Iron Thorn [EPUB ebook] 

Honor White Jackson was a human being. But his planet was not Earth, nor his time Now. His world was dominated by a giant Iron Thorn. Beyond the reach of this tower there was supposedly, nothing — except a frozen, airless desert where huge winged beasts called Amsirs roamed. The duty of Jackson’s caste was to hunt and kill the Amsir. And it was not until Jackson had made his first kill that he discovered the secret of his world. As the creature lay dying at his feet, Honor White Jackson partook of the fruit of knowledge. Forevermore he was committed to another life — and the bitter discovery of genius, cruelty and the human paradox.