Fathom

The ageless water witch Arahab has been scheming for aeons, gathering the means to awaken the great Leviathan. She aims to bring him and the old gods back to their former glory, caring little that their ascendance would also mean an end to the human race. However, awakening the Leviathan is no small feat. In fact, Arahab can't complete the ritual without human aid.
Arahab's first choice is Jose Gaspar, a notorious sea pirate from eighteenth-century Spain. But when the task proves too difficult for Gaspar, she must look elsewhere, biding her time until the 1930s, when the ideal candidate shows up: a slightly deranged teenager named Bernice.
Bernice is sophisticated, torn from New York and forced to spend a miserable summer on Anna Maria Island, a tiny rock off the coast of Florida, She's also been saddled with the companionship of her farm-raised cousin Nia. Eventually, Bernice's disenchantment gives way to rage, which in turn leads her to commit a deadly crime. When Nia won't cover for Bernice's actions, she turns on Nia, chasing her into the deadly coastal waves.
The timing is right and the elementals have better ideas: The moment the girls go under, Bernice is commandeered for Arahab's task force and Nia is turned into a strange and powerful new creature by a servant of the earth who doesn't want to surrender his green fields and muddy plains - not yet, at least. Add in a hapless fire inspector who's just trying to get his paperwork in order, a fire god whose neutrality has been called into question, and a bizarre religious cult, and rural Florida doesn't seem quite so sleepy anymore.