| Director | Choi Dong-hun |
|---|---|
| Genre | action film, fantasy film, science fiction film, time-travel film |
| Runtime | 142 min |
| Country | South Korea |
| Budget | $25 million |
| Box office | $12.1 million |
After a short prologue, the plot moves to the modern day and then back to fantasy Goryeo, though scenes from the two time periods are interspersed.
In a prologue set in 1380 A.D., monk warriors attempt to defeat an alien and its human host but fail. Guard and Thunder, two humanoid robots, arrive from the future and successfully extract the alien from its host. Before dying, the former host asks Guard to take care of her baby, but he explains that they cannot interfere in human affairs. Guard and Thunder return to their home base in the modern day, but upon their return, Guard discovers that Thunder has smuggled the infant back with them.
Guard raises the baby girl, Lee Ahn, without revealing his true identity (Thunder is disguised as their family SUV). Relying on her memories of Thunder talking to her when she was an infant, Lee Ahn becomes increasingly suspicious of Guard and discovers more and more of the truth about Guard, Thunder, and how she came to live with them.
Lee Ahn finds her way to Jisan Hospital, the site of an incoming alien prisoner transport. Guard and Thunder explain the mechanics of alien imprisonment: when an alien prisoner is injected into a human host, it remains confined to its host's subconscious — the human loses their memories of the implantation and does not know they are a host. The alien's consciousness can be awakened under certain circumstances, such as breathing in haava (the atmosphere of their native planet) or being cut by Guard's knife-shaped power source. Aliens can only survive in Earth's atmosphere for five minutes, after which they must either return to their original host, or move to a new host (in which case they again lose consciousness). It is hinted that the host can become aware of the prisoner even without an external mechanism, as happened in the prologue.
Shortly after the transport ship deposits its prisoners and departs, a prisoner-aligned alien ship arrives on Earth. Its pilot plans to awaken the Controller using Guard's power source, then release the concentrated haava on board the ship to transform Earth's atmosphere — this would simultaneously awaken all of Earth's alien prisoners and poison all of humanity. The pilot succeeds in awakening the Controller and releasing one sphere of haava, devastating several city blocks and awakening two other alien prisoners.
Guard, Thunder, and Lee Ahn work together to kill the alien pilot and prevent the Controller from releasing the remaining haava on board the ship. The battle leaves the three aliens, Guard, and Thunder badly wounded outside the ship, with a timer counting down to the haava release. Out of time, Lee Ahn hatches a desperate plan to travel back in time, luring the aliens back with them, then shake them off and maroon them in the past before returning to the present to stop the countdown. They execute the plan and all three aliens follow them into the past. In a final battle, Guard is destroyed, Thunder (in SUV form) sinks to the bottom of a river, and the Controller is badly wounded and forced to abandon its host.
Ten years after Thunder crash-lands in the past, a Taoist bounty hunter named Mureuk decides to pursue a huge bounty for a mystical knife called the Divine Blade, which is eventually revealed to be Guard's knife-shaped power source. Despite his unserious demeanor, Mureuk appears to have incredible talent for magic and martial arts, with an especially remarkable ability to recover from serious injuries.
While pursuing the Divine Blade through various misadventures, Mureuk meets various legendary figures of the martial arts world. Among these figures are the Monk Guru, a high-tier Taoist; the Dual Mages, a pair of inventor-mages with an arsenal of strange magical items; and Dogturd, an unremarkable figure who knows some gossip and points Mureuk in the right direction. He also meets the Girl Who Shoots Thunder, who turns out to be Lee Ahn (her "thunder" is a pistol), and Suiter and Ja-jang, the two aliens from the future who have taken over a local cult. If either Lee Ahn or the aliens obtain the Divine Blade and Thunder's location, they can return to the future and either complete or stop the haava release.
As these figures converge on the Divine Blade, they descend into a chaotic battle. Lee Ahn manages to lure one of the aliens away, while the other is defeated; Lee Ahn shakes off her pursuer while drawing closer to Thunder's location at the bottom of the river.
Near the end of the film, it becomes clear that Monk Guru, the Dual Mages, and Dogturd have something else in common that caused them to be targeted by the aliens: they were all nearby when the aliens crash-landed in the past, and are therefore candidates to be the new unconscious host of the Controller. However, unbeknownst to the aliens, there was a fifth person present: Mureuk, Monk Guru's young apprentice. Mureuk rescued Lee Ahn from the river and the Controller took him as its new host, causing him to lose his memories of the incident; the film ends on this revelation.