A homebody named Su Yan accidentally clicks on an online ad and stumbles into the demon world's capital city, Linyuan. Unexpectedly, he somehow becomes a demon king who doesn't know anything about magic. In order not to let others find out that he's a powerless pushover and get himself killed, Su Yan decides to fawn on the powerful General Hua, whose power is only second to that of the Demon King.
However, it turns out that General Hua is also a person who has traveled through time and space from the modern world. So the two moderners begin their journey of leveling up and battling monsters together in Linyuan City. They tame the mount, Silver Dragon, and outwit the demon world's high-ranking officials while concealing their identities. On the once-in-300-years Dengming Assembly, they promote talks between the monster clan's Young Master Ying Ri and the immortal realm's Lord Lu Zhen to forge peace across the three realms.
Moreover, they manage to find the magical bead to restore the primordial spirit of Yu Ke, Su Yan's rebellious and cunning younger brother. However, the disappearance of the magical bead leads to chaos in Linyuan City, threatening to destroy the demon world and forcing Su Yan to finally make the most important decision as the Demon King.
