Deeplight
(Book)

In an alternative world, fifty years after the death of the gods, a fifteen-year-old boy, Hark, finds the still beating heart of a terrifying deity and uses it to try to save his best friend. Hark risks everything to keep the heart out of the hands of smugglers, military scientists and secret fanatical cults, to try to use it to sustain the life of his best friend, who is gradually and eerily transforming. But how long should someone stay loyal to a friend who is himself becoming a monster?