The water-covered world of the Swell has been ravaged by the incursion of the moon shards as they make their way through the endless oceans, corrupting and transforming everything in their path. With little information and no clear direction, the remaining pockets of humanity press forward to retain what life they have on the dangerous waters. Enchanted sea glass is still the key to humanity's survival, but there are some who would seek to exploit the celestial objects for their own cause.

Vila Del'Sor has joined forces with what's left of the Deep Wardens to discover the secrets of the corruption and bring the refugees of the Planks to safety. Her choices are complicated by the arrival of a new Warden: one who wears the face of her most hated enemy and claims to have information that could help in the quest for understanding the corruption.

Deep below the surface, Narrio Olitarth is not having a good time in the underwater prison of Grim-Mire Hold. Terrible meals, unpleasant company, and life-threatening injures are only a few of the issues he faces as he carries out his new sentence. Escape is impossible from the legendary prison, but Narrio is determined to find a way–if he can survive that long.

Meanwhile, all is not well for Bal De Bao, a young Oceanid from Boola's Reach. The Oceanid culture is one of rules and regulations meant to protect and provide for the underwater society, but Bal is tired of rules and regulations. As an offspring from Farmer Craft begetters, Bal is on the search for something greater to do with their life. But when that opportunity comes, Bal is forced to reckon with their changing worldview and consequences for their actions–consequences they did not realize were ever on the table.

The corruption spreads slowly, but the full moon's rise is approaching again. Mysterious forces are at play, machinations are in motion, and no one seems to know what's going on.

Welcome back to the world of the Swell. Welcome to the Tainted Seas.