Detective Dee (Mark Chao) heads the Bureau of Investigation in Tang Dynasty China; as a result of his protection of the kingdom earlier (in "Detective Dee and the Mystery of the Phantom Flame," 2010) the Emperor entrusts to him the Dragon Taming Mace, a weapon so powerful that it will serve to save the nation if needed. Unfortunately, the Empress (Carina Lau) doesn't trust Dee and, really, wants to assume complete power for herself, so she instructs one of the royal guard, Yuchi (Feng Shaofeng), to steal the Mace from Dee, knowing that Yuchi and Dee are long-time close friends and relying upon that friendship to turn to betrayal. Meanwhile, there are a number of clans of wizards who use illusion and sometimes magic to further their own ends, in particular to overthrow the Tang Dynasty....The above description only covers the relatively "normal" part of the story; throw in a bunch of seriously ugly monsters, a heavy dose of wuxia martial arts (fighters climbing the air as if it was a staircase, etc.), an extremely serene Buddhist, a totally unhinged Empress and, well, a love story between a doctor and an assassin, plus tons of sword fights and action all over the place, and you have the latest Detective Dee tale. By the way, the Four Heavenly Kings of the title feature in exactly one scene as statues, some of which are destroyed in the scene, and are never mentioned again. Go figure. I liked it all, a fitting end for 2018's Montreal FantAsia Film Festival for me!