Two sisters live along the coast. Their windows are lit with lanterns, for one is a witch the sea spat back to shore, and the other is still finding her way home.

Maren is the first to take in a poor young man washed into their harbor during a raging storm. She takes him not to her own lonesome cottage, but to that of her sister. Many months have passed since Vivian herself was spit back from the sea, her eyes faraway and words stolen from her lungs. With their strange new patient, Maren will need the extra help, and perhaps find her way back to her sister in the process.

But their poor drowned sailor is not merely a man lost at sea. Plagued with dreams of monsters from the depths and Vivian's ominous hints, Maren must unwind the mystery of his origins while strange scales appear on the moors, livestock are attacked by unknown teeth, and the growing storm threatens to tear their small village from the cliffs.