Paleontology researcher Lin Yuan accidentally time-travels to the Cambrian period, turning into a one-centimeter trilobite and binding with the Active Evolution System. In the dangerous primordial ocean, he devours prey to gain energy and continuously unlocks evolution options, successively acquiring body structures like giant pincers, venomous blades, and wing fins. He dodges anomalocarids, battles hunsgiacaris and eurypterids, and chooses low-temperature dormancy to combat memory loss. Awaken after tens of millions of years, the ocean is already the age of fish; Lin Yuan merges with fish bodies, hunts dunkleosteus above his level, and creates reconnaissance clones. Finally, he encounters a powerful five-meter ethereal ammonite, engaging in a desperate battle with it. After the fierce fight, a mysterious anomaly comes from inside the ammonite's corpse.