Byeong-gu, a whimsical yet tormented man, is convinced that extraterrestrials from Andromeda PK 45 are poised to invade Earth, and he believes he is the sole protector of humanity. Accompanied by his playful circus performer girlfriend, Su-ni, he devises a desperate plan to kidnap a high-ranking pharmaceutical executive, Kang Man-shik, whom he suspects to be a powerful alien capable of contacting the Andromedan prince during an imminent eclipse.
As they imprison Man-shik in Byeong-gu's basement workshop, he resorts to torturous methods, initially trying to disrupt the supposed alien's communication with a Korean liquid painkiller, mulpad, which contains chlorpheniramine maleate, and by employing a “Italy towel" commonly used by Korean Ttaemiris. However, the situation takes a darker turn when it appears that Byeong-gu's mother was a victim of his captor’s company, poisoned in a pharmaceutical trial. This revelation unveils the depths of Byeong-gu's madness, revealing not just a childlike delusion but also a fractured psyche driven by a desire for vengeance.
When a detective arrives to investigate the executive's abrupt disappearance, the encounter becomes increasingly volatile. Man-shik's attempts to flee are thwarted by Byeong-gu's erratic behavior, while the detective initially finds nothing amiss due to Byeong-gu’s efforts to cover his tracks. However, as the detective exits, he spots Byeong-gu's dog, fittingly named Earth, gnawing on the remains of Byeong-gu’s previous victims. The detective soon meets a gruesome fate at the hands of Byeong-gu's pet bees, leaving Byeong-gu to escalate his horrors by crucifying Man-shik and breaking his leg in an act of punishment.
A glimmer of hope arises when the executive slyly convinces Byeong-gu that a bottle of benzene in his car is the antidote for his mother’s comatose state. Rushing to the hospital with this newfound purpose, Byeong-gu leaves Man-shik alone, who seizes the moment to free himself from his restraints. Venturing deeper into Byeong-gu's chaotic domain, the executive discovers unsettling evidence of Byeong-gu’s chilling experiments, including photographs of dismembered bodies and notebooks covered in blood. The pages detail Byeong-gu's tragic past: a father who lost an arm in a coal mining accident and was ultimately killed by the family, a mother poisoned in a neglectful drug trial, and violent childhood experiences that left a mark on his psyche. These layers of trauma culminate in the man Byeong-gu has become.
As chaos unfolds, the dead detective's partner finds the frantic executive just as Byeong-gu, in a blind rage, arrives home only to find the detective there as well. A tumultuous struggle ensues, and in a shocking twist, the executive claims to be an alien, spinning a fantastic tale of his kind's efforts to save humanity from a destructive gene since the time of dinosaurs. This bizarre confession serves as a ploy to buy time, positing that he can yet contact the alien prince at the pharmaceutical factory.
Leaving his fate in the hands of the detective, Byeong-gu rushes to the factory where the executive devises a deadly scheme involving a robotic arm meant to eliminate Su-ni. In a dramatic confrontation, Byeong-gu is brutally beaten, and as law enforcement arrives, they shoot him. In his final moments, bloodied and dying, he laments, >“Now who will save the earth?”
In a shocking conclusion, it is revealed that the aliens are indeed real, beaming the executive aboard their vessel, only to unveil that he is the alien king. Fed up with humanity's corruption and cruelty, he deems Earth a failed experiment, obliterating it from existence. As the credits roll, still photographs provide a poignant contrast, showcasing the fleeting moments of happiness in Byeong-gu's life, framed by his relationships with his father, mother, and Su-ni.
