Accidentally time-traveling into the turbulent demon world of Great Jing, Jiang Lan not only becomes a handyman of the Town Demon Office, but also unexpectedly activates the Town Demon Merit System. He saves the dragon half-demon sisters Lin who are ostracized by the world, and relies on the system to diligently study martial arts, exterminate haunting demons, uncover the conspiracy of the Blood River Holy Sect, and grow through experiences all the way. While protecting his family and the peace-loving common people, Jiang Lan explores the heavy secrets of the dragon bloodline and the old case of Mirror Lake, fights against various evil forces, and shoulders the heavy responsibility of guarding a region.