Meri and Aodhan have been through a lot over the past few months—vengeful gods, creatures that can remove your free will with a touch, and the schemes of Ker Ys's rulers—and they weathered it all in stride. Now Meri's birthday is approaching, and the two of them finally feel like they can relax, and plan their future together.

But their enemies won't go quietly. Corentin, the crown prince of Ker Ys, puts a plan in motion that rips Meri away from her family and lands her in the middle of his plot to make his homeland the most powerful of the sea kingdoms—but in order for his plan to work, he'll need to conquer Kilstiffen. Meri has other ideas, and calls in every favor she's owed, from a stone merrow that once gave her a key, right on up to Manannán mac Lir, the sea god himself.

Even with such powerful allies, Meri ends up trapped at the bottom of the ocean. Surrounded by cold saltwater and villains in the guise of friends, she only has herself to rely on—herself, and a pearl pendant with the power to change fate.