Deeplight

Enter a fantastical, underwater world in Deeplight, from Frances Hardinge, the Costa Award-winning author of The Lie Tree.
The gods of the Myriad were as real as the coastlines and currents, and as merciless as the winds and whirlpools. Now the gods are dead, but their remains are stirring beneath the waves . . .
On the streets of the Island of Lady's Crave live 14-year-old urchins Hark and his best friend Jelt. They are scavengers: diving for relics of the gods, desperate for anything they can sell. But there is something dangerous in the deep waters of the undersea, calling to someone brave enough to retrieve it.
When the waves try to claim Jelt, Hark will do anything to save him. Even if it means compromising not just who Jelt is, but what he is . . .