The year is 2022, and Guard and Thunder are living on earth while managing alien criminals imprisoned in human bodies. One day, a mysterious spaceship appears above Seoul, and detective Moon Do-seok witnesses the strange occurrence. Meanwhile, in Goryeo 630 years ago, the hack of a guru Mureuk and the lightning-shooting woman Lee Ahn compete with each other while tracking a legendary sword for a bounty. The two spirits Heukseol and Chungwoon discover the secrets of the sword, and the masked Jajang also joins the race. Here, another spaceship rises from a river deep in the mountains.