The decisive Battle of Zhuolu comes to an end as Huangdi and Yandi join forces to slay Chiyou, bringing the Jiuli tribes to defeat and establishing the first peace in the Central Plains. However, Chiyou's lingering spirit remains. The Great Priest of the Jiuli leads the surviving forces into the desolate wilderness of the southern frontier, where they use witchcraft to awaken ancient ferocious beasts one after another, including Zhuhai, Zhaochi, and Gudiao. They set an ambush in Soul-Severing Valley, plunging the southern frontier into war. As the conflict escalates, Hundun, one of the four great ancient beasts, breaks free from its seal. Xiangliu, the ferocious beast under the command of the Water God Gonggong, emerges with the power of ten thousand poisons. The Yan-Huang allied forces face one perilous battle after another. Only with Yinglong's reinforcements and fierce battles against the strange beasts can they barely stabilize the situation. But when Gonggong's lingering consciousness awakens, it triggers a complete eruption of the underground water veins. Catastrophic floods sweep across the Nine Provinces, turning the lands of the tribes along the middle and lower reaches into vast lakes.