Zhang Xiaoman, a young man from Tianjin, accidentally travels back 3.5 million years to East Africa. After narrowly escaping becoming prey to wild beasts while running around naked, he is rescued by an ancient ape named A Li. Relying on hints from a mysterious system, he learns to master fire. With his quick wit and modern knowledge, he uses barter to gather a group of struggling ancient apes, confronts outside enemies, and survives devastating floods. As the secrets of a mysterious black stone and time travel gradually come to light, he encounters another time traveler. Giving up his chance to return to his own era alone, he chooses to build his tribe and unlock a mission that will allow two people to return together. The ending reveals a chilling hint that their world may be part of a civilization experiment.