An unnatural fog, lingering for weeks, has settled over the Stockholm archipelago, home to twelve-year-old Tuva. No one can explain it. Tuva, attuned to the mysteries of the sea, has her suspicions.

When her classmate and his mother nearly drown in the damp, choking fog, Tuva seeks answers about its supernatural nature. And the truth she uncovers is more wondrous—and sinister—than she could have imagined.

All the while, a hauntingly familiar voice calls for Tuva, pulling at the ties that bind her to the supernatural world, trying to draw her in. But are the powers that Tuva possesses enough to save the world from this true evil lingering in its midst?