On a summer night in 1995, Lin Xu, a graduate of the international trade department, clutches a bloodstained ship's log as he encounters a bizarre shipwreck at Ghost Head Reef, where his father disappeared. When a sextant pierces his palm, an eerie blue screen bursts into view: [Canghai System activated. Host DNA matches that of Ming dynasty sea merchant Lin Daoxuan: 99.7%]. But this golden finger, which grants him sonar detection and the ability to communicate with marine life, only draws him deeper into the fog: the lighthouse keeper Uncle Chen's hesitant gaze, developer Zhao Tianba's excavators surrounding the fishing boats, and the words circled in blood in the log: “High tide at the hour of the Rat on the fifteenth day of the seventh month.”
Guided by the System, Lin Xu takes up his father's unfinished longline fishing business, only to haul up a Ming dynasty celestial globe engraved with a star map in his net. When the instrument resonates with an abandoned lighthouse on the seabed, it projects the magnificent phantom of a Dragon Palace beneath the coral reef. Ecological technology buried by Zheng He four hundred years ago is awakening. But with every shipwreck dock he unlocks, Zhao Tianba's gambling boat edges ten miles closer to international waters. During a midnight dive, Lin Xu discovers that a construction crew is pouring concrete pilings mixed with Japanese pirate ashes into the seabed.
As the firefly coral that can purify seawater comes back to life, threats follow one after another: mutated octopuses devouring fishing nets, a Spanish ghost ship appearing in the eye of a typhoon, and a bronze door deep inside the Dragon Palace engraved with Lin Xu's birth details. The System keeps warning him: [Mantle pressure at 97%]. Meanwhile, the model ship left behind by his father assembles itself into a map of the seabed city's defenses. When Zhao Tianba detonates land-reclamation explosives and triggers a tsunami, Lin Xu has no choice but to activate the ultimate protocol at the Dragon Palace altar: anchor himself there, linking the entire East China Sea ecosystem to his own nerve endings.
