Like any teen thrust into the world of adult responsibility, she shies away from her calling. She hides the jewel and sets herself, and her family, down a tortuous path.

“I definitely consider this a coming-of-age story,” says Johnson, on the phone from New York. “It begins with that classic moment: The girl gets her period. It speaks to a certain age where you’re biologically an adult, but you aren’t emotionally.”

In vintage fantasy-fiction–style, Lana’s betrayal of the elders and the spirits—dark forces that rule the island with invisible hands—cannot go without consequences. She leaves her home island to apprentice with a one-armed witch named Akua, who trains Lana in a strange and powerful sacrificial magic. It’s not long before Lana finds herself in a position to use that magic, without fully understanding the extent of its power.

At times, the multifaceted plot feels as though it could get away from Johnson, but she’s able to rein it in at the right moment. It’s a highly imaginative tale that embeds the story with enough action to appeal to the young-adult crowd, and enough ideas for their parents.

“There’s something both liberating and exacting about taking things out of the real world and setting up a thought experiment,” Johnson says. “Fantasy has a unique ability to create a new world and then add truth to it.”

All the themes of a coming-of-age novel are here: the fear of adulthood; the increasing complexity of relationships; the stuttering first attempts at making important, life-altering decisions.

“[Author] China Miéville said that fantasy is the only genre where the metaphors can be both literal and figurative,” she says. “So in, say, Buffy the Vampire Slayer, high school is literally and figuratively hell.”

That’s also true about Racing, in which the island culture is endangered by the spirits—natural disasters pound the village and the mandagah fish are dying off.

It’s perhaps this aspect of the book that cuts the deepest. In a time when islands are under constant threat from increasingly strong storms, and whole coastal economies dependent on fish are finding their oceans bankrupt, the metaphor of an ever-dwindling population of bountiful fish is not lost.

“When I first started writing the book, I started writing it about Japan,” Johnson says. “I’d studied abroad there, and something about living in a place completely isolated and surrounded by water was so evocative.”

Johnson sees the story as unresolved. She’s working on a sequel, and views Racing as the first in a trilogy. “I have the second book pretty well blocked out. The third is still up in the air,” she admits. “It’s a little scary. There are a lot of threads that I’ll have to tie up, and with the first book out, you can’t go back and change anything. It’ll be interesting to see.”

Racing the Dark (Agate, $24.95) is out now.