Every three years the pirate cities perform a sea rite that offers a noble girl to the god Nereus, binding him to hold back the dark god Cthaken. Laren, whose blood carries Cthaken's mark and who can reshape his features, takes his sister Lian's place as the bride. In return for three years of pretense, he is promised freedom and a fleet. Inside the sea palace, Nereus favors the siren Ison and ignores Laren's suffering, while sabotage follows him everywhere.
Once free, Laren flees to the free port, falls for the adventurer Karen, and turns down a remorseful Nereus, who learns the truth only after Laren has left. A cultist named Evan frames Nereus for Karen's death to wake Cthaken within Laren, and the dark god breaks loose and ravages the land. Nereus gambles on an outlawed spell that rewinds the world, and the sacrifice ritual vanishes.
