Lindsay, portrayed by Ashley C. Williams, and Jenny, played by Ashlynn Yennie, are two American tourists venturing through Germany who encounter a series of horrifying events. While attempting to reach a local nightclub, their car unexpectedly breaks down in the dense woods. Reluctantly refusing a ride from a menacing truck driver, the pair set off on foot in search of help as rain begins to pour. Their journey leads them to a secluded countryside house, which is owned by the deranged surgeon, Dr. Heiter, played by Dieter Laser.
Under the pretense of making a phone call, Dr. Heiter deceives the young women by offering them what he claims is water, but is actually drugged. Their next memory is awakening in a makeshift medical facility located in the house's basement. In a terrifying twist, they witness Heiter executing a kidnapped truck driver named Rene de Wit, remarking that the man is “not a match” for his gruesome experiments. When they regain consciousness a second time, they find themselves alongside another unfortunate captive, Katsuro, a Japanese tourist.
Dr. Heiter reveals his horrifying ambition: he prides himself on being a world-renowned specialist in separating conjoined twins, yet he dreams of creating new, monstrous beings that share a single digestive system. He horrifically outlines his plan to surgically connect his three captives, arranging them in a grotesque manner of "mouth-to-anus." After Lindsay makes a desperate attempt to escape, Heiter decides to punish her by making her the central part of his repulsive "human centipede" experiment.
As the surgery takes place, Heiter tries to bond with his creation, amusingly training them like pets, which culminates in Lindsay enduring the horrific act of swallowing Katsuro's waste. However, the situation takes a dire turn when Jenny's health deteriorates due to blood poisoning stemming from the brutal operation.
Days later, local detectives Kranz and Voller arrive to probe the disappearances of tourists in the area. In a chilling moment, Heiter plans to make them his next victims. Initial attempts to poison the detectives fail, forcing them to seek a search warrant and leave the house. Meanwhile, the captives make a desperate but futile escape attempt, and Katsuro confronts Heiter, revealing his guilt about past family transgressions before taking his own life.
As dramatic chaos ensues, the detectives return to the house, conducting searches that lead to a series of violent confrontations. Heiter’s gruesome games of cat-and-mouse culminate in a deadly showdown, leaving several casualties in their wake. Ultimately, their grim saga concludes with Jenny and Lindsay holding hands in a bittersweet moment of connection as life slips away from Jenny due to the infection. Despite the knowledge that their captor has met his end, Lindsay finds herself left alone, forever trapped in the grim house, positioned between the lifeless bodies of her fellow victims.
