In a dystopian 21st century, society imposes strict restrictions: sexual intercourse and reproduction are forbidden, while the consumption of mind-altering substances is mandated to maintain control over the populace. Emotions, relationships, and even the very idea of family are deemed taboo. Citizens wear identical uniforms and have shaven heads to symbolize their enforced equality, contrasting with the police androids who don black uniforms and the robed monks. Instead of personal names, individuals are assigned a three-letter designation followed by a four-digit number, which is displayed on their identity badges at all times.
As the narrative unfolds, we meet SEN 5241 and LUH 3417, who are responsible for overseeing the city's surveillance from their posts in central video control centers. LUH shares a living space with THX 1138, a factory worker engaged in the production of android police officers. At the story’s onset, THX, while enduring an incessant call for increased safety—celebrating a relatively low worker casualty rate of 195 compared to a rival factory's 242—decides to leave his job.
On his journey home, THX stops at a confession booth, diligently murmuring prayers under the portrait of “OMM 0000”. A calming voice assures him, concluding each confession with, > “You are a true believer, blessings of the State, blessings of the masses. Work hard, increase production, prevent accidents, and be happy.”
Upon returning home, THX engages with holobroadcasts while under the influence of prescribed drugs and even utilizes a device for self-gratification. Meanwhile, LUH illicitly replaces THX's drugs with pills she possesses, which leads to THX experiencing both physical discomfort and confusion. This act also sparks a romantic bond between them, culminating in their first physical intimacy.
Things take a turn when THX is assigned with SEN, who becomes his new roommate. However, a complaint against SEN regarding an illegal housing arrangement creates chaos in THX’s life. The absence of his usual drugs leads him to struggle during a critical work assignment, prompting a "mind lock" that heightens the risks at his job. When released from the mind lock, THX manages to rectify his performance, but it's too late: both THX and LUH find themselves arrested.
In a brief moment of hope, THX and LUH reconnect, only for her to reveal she is pregnant. Their fates soon collide at THX's trial, resulting in a prison sentence for both him and SEN. While many inmates exhibit no interest in escaping, THX and SEN ultimately discover a way out, subsequently joined by SRT 5752, a holographic character from the holobroadcasts.
As the trio attempts to flee, they become separated from SEN, who wanders into a child-rearing area but soon falls into the hands of police androids. In a desperate twist, THX and SRT steal vehicles but encounter disaster when SRT crashes into a concrete barrier during their escape. With police androids hot on their heels, THX races to the outskirts of the city and dives into a ventilation shaft, narrowly evading capture as Central Command orders the termination of pursuit due to budget constraints.
In a stunning revelation, it is unveiled that their entire city is situated underground. Finally emerging onto the surface, THX beholds the mesmerizing sunset, a sight that symbolizes freedom and the profound beauty of the world beyond the confines of their oppressive society.
