Major Kang Min-gil Kim Seung-woo leads a secretive mission as high-level North and South Korean leaders debate the surrender of a secretly designed 50 Mt nuclear warhead, a weapon kept in a hidden underground bunker near the DMZ. Faced with escalating international pressure, the two sides agree to hand over the device and shut the facility, but Kang’s disillusionment with reconciliation pushes him to defy the orders and steal the warhead with a cadre of loyal soldiers. In response, the South deploys a Naval Special Forces platoon under the command of Park Jung-woo (Major Park Jung-woo) to retrieve it, setting the stage for a dramatic collision of eras and loyalties.
A tense pursuit unfolds on the water as the modern platoon corners Kang and his squad, plunging into a firefight that is abruptly interrupted by a celestial anomaly. A comet roams unusually close to Earth, triggering a time rift that folds the present onto a distant past within the comet’s 433-year cycle. From 2005, three modern Koreans and a female scientist, Dr. Kim Su-yeon Gong Hyo-jin, are hurled back in time alongside the missing warhead, landing in 1572 in the midst of a brutal clash between Joseon-era Koreans and ruthless Jurchen invaders.
The newcomers encounter Yi Sun-shin Park Joong-hoon in an unlikely and jarring transformation: the legendary admiral-to-be is here a scrappy, self-preserving thief and ginseng smuggler who has just failed his Gwageo examination. He has even hidden the modern soldiers’ small arms, having no sense yet of the history around him. A young peasant girl nearby uncovers one of the handguns as she tries to hide from pursuing Jurchen spies, and from that moment the “Heavenly Soldiers” nickname—born of their puzzling and seemingly magical abilities—begins to take hold.
Major Park attempts to impart military discipline and strategy to Yi, hoping to shape him into a true commander, while Kang and his squad continue to search for the missing warhead. The Jurchens, wary of this inexplicable force, close in. The North Koreans come across Yi again, release him from a perilous bind, and ultimately recover the warhead within a war leader’s tent. In a brutal turn, Kang is forced to kill the son of a local chieftain, provoking a fierce counterattack from the Jurchens who mobilize to purge the “Heavenly Soldiers” from the land.
With the warhead secured and the timing of the comet precisely calculated by Dr. Kim, the modern Koreans prepare to depart the past. Yet Yi—seeing the cruelty inflicted on the villagers—summons the resolve that has long eluded him and joins the effort, bringing the elders and the villagers’ plea to the forefront. Park and Kang debate tactics, and Yi advocates a pragmatic blend of ambush and a resolute last stand that could safeguard the people who have befriended them.
That night, just before the comet’s closest approach, Park urges Yi to save his own life as well, but Yi resists and is knocked unconscious, carried away by the others. Kang, knowing he will be hunted once they return to the present, chooses to return to the village to defend it; the remaining modern soldiers stay behind for their own reasons as well. In a dramatic turn, Yi escapes confinement, rejoining the Heavenly Soldiers and the villagers in a protracted battle against the Jurchens. The invaders eventually falter, suffering heavy losses, but only Park, Choi Gwang Kim Seung-cheol—the North Korean sergeant—and Yi survive the confrontation alongside the remarkable admiral-in-waiting.
Dr. Kim and the warhead succeed in returning to the present, where she reports the team’s moral and physical sacrifices to the Korean generals. Yet the authorities, bound by political caution, decide to turn over the warhead rather than honor the soldiers’ selfless deeds, closing a circle that juxtaposes modern diplomacy with ancient courage. In the film’s final gaze, Dr. Kim visits a memorial to Admiral Yi, and the narrative cuts to the opening moments of the Battle of Myeongnyang Strait. Aboard Yi’s flagship, the great commander—still aware of the proverb “in life there is death, in death there is life”—gives the order to charge, with Park Jung-woo and Choi Gwang at his side as trusted staff, signaling that courage and cunning can shape a nation’s future even when history itself seems to bend.
