Something ancient waits beneath Blackwater Harbor-and it knows his name.

Gabriel Vale has spent years keeping Hollowmere's lighthouse burning through every storm. The light protects the town, steadies the harbor, and helps keep something old and dangerous asleep beneath the water.

Then Celia Ward appears barefoot on Blackwater Pier during a storm, soaked in seawater, missing pieces of her memory, and somehow connected to the thing stirring below the harbor.

Gabriel knows he should send her away.

Instead, the harbor reacts when they touch.

As storms gather over Hollowmere, the lighthouse fails, figures come ashore from the fog, and Celia begins to remember black water, voices beneath the waves, and a presence that may have allowed her to survive for a reason. The closer she gets to Gabriel, the harder it becomes for him to control the darkness inside him-and the clearer it becomes that the harbor wants them both.

To save Hollowmere, Gabriel and Celia must uncover what was buried beneath Blackwater Harbor before the ancient thing below rises completely.

But some monsters do not stay buried.

And some lights are not meant to be opened.