When the deep sea begins to speak, the land must learn to listen—or it will remain silent forever.
Sixty years ago, the Agor civilization fell into the "Great Silence" overnight, and seven coastal mobile cities evaporated. Sixty years later, abnormal events began to reappear in the Iberian waters: scientific research platforms mysteriously lost contact, deep-sea samples showed traces of artificial modification, and mysterious armed forces calling themselves "Coast Watchers" began to systematically salvage the sunken Agor ruins.
Rhode Island received a request for help from Leitanian oceanographer Otto von Essenberg, but found himself involved in a conspiracy that spanned the deep sea and land. The deep-sea hunter Skadi, who was once thought to be dead, suddenly returns, leaving a warning: "The Daughter of the Tide is back"; the Glasgow gang intercepted a transport convoy carrying Agor's consciousness container at the border; and Dr. Kelsey's secret agreement with Agor's envoy Ethel sixty years ago is gradually coming to light.
The investigation found that the Agor people did not disappear, but sank the entire civilization to the bottom of the ocean as a living seal imprisoning seven "ancient beings". Today, these seals, called "locks", are being destroyed one by one - the masterminds behind this are the fallen Agor warlocks who call themselves the "Eye of the Deep Sea" and their human collaborators, the "Coast Watchers". They plan to open all the seals and welcome the return of the imprisoned, even if the price is the end of land civilization.
"Prisoners should stay in cages." - But what if the cage itself begins to long to be opened?
