Deeplight — Frances Hardinge

“Equal parts dazzling fantasy, swashbuckling adventure, and tender coming-of-age tale” from the author of the Costa Book of the Year, The Lie Tree (Publishers Weekly, starred review).
 
The gods are dead. Fifty years ago, they turned on one another and tore each other apart. Nobody knows why.
 
Now, even coin-sized scraps of dead god are worth a fortune because of the strange powers they're said to possess. But few are brave enough to dive and search for them.
 
When fifteen-year-old Hark finds the still-beating heart of one of these deities, he'll risk everything to keep it out of the hands of smugglers, scientists, and cults who would kill for its power. Because Hark needs the heart if he wants to save the life of his best friend, Jelt. But the power of a god was not meant for human hands.
 
With the heart, Jelt begins to eerily transform, and Hark will have to decide if he can stay loyal to his friend -- or what he's willing to sacrifice to save him.
 
“Hardinge is assured and sophisticated in her exploration of the dark temptations of power.” -- The Wall Street Journal
 
“Monsters and mortals collide in this fantasy adventure that explores the hypnotic allure of fear, the adamant grip of the past, and the redeeming power of stories . . . Thrilling.” -- Kirkus Reviews (starred review)
 
“Glorious thematic complexity inhabits a wildly inventive world, with the menacing roils of a dangerous sea threatening the archipelago and touches of steampunk rounding out the fantastical elements . . . Readers will be thrilled to be pulled into the alluring expanse of her work.” -- Bulletin of the Center for Children's Books (starred review)