Insane

During a daytime walk downtown, Soo-Ah is unexpectedly seized and whisked away by unknown captors. She is brought to a psychiatric hospital run by the sadistic director Jang Hyung-sik. The staff refuse to explain why she was detained, and they begin administering coercive medications to break her will.

Soo-Ah is admitted to the psychiatric hospital where doctors and staff subject her to intimidation and forced medication. She is threatened with harm if she resists, and she begins to realize she has no one to turn to. In these early days, she starts to jot down notes about what she endures.

She secretly writes down every atrocity she witnesses, detailing the brutal acts carried out by the facility. The act of journaling becomes her only defense and a potential record for later truth. Her writings gradually become a lifeline amid the cruelty around her.

After attempting to resist or escape, Soo-Ah endures severe torture as punishment. The director and staff escalate their cruelty to crush her spirit, setting the stage for her resolve to survive and reveal the truth.

An orderly named Dong-sik grows fed up with the inhuman treatment and contacts Soo-Ah's boyfriend Woo-Jin to plan a rescue. Meanwhile, Mi-ro accidentally sets Hyung-sik's office on fire, triggering chaos. Dong-sik informs the others and Mi-ro helps the escaping trio, though he stays behind to rescue the remaining captives.

As Soo-Ah and Woo-Jin attempt to flee, Hyung-sik, badly burned, pursues and drags Woo-Jin away, and both perish in the blaze. The escape collapses, and Soo-Ah is left to flee the burning facility on her own.

Soo-Ah escapes the facility and returns to her house, only to find her abusive stepfather dead from a gunshot wound. The shocking discovery ties her personal trauma to the wider violence surrounding her fate.

Despite her innocence, Soo-Ah is arrested on suspicions of murder and arson related to the hospital fire. The case marks a turning point that propels her into the broader investigation of the hospital’s crimes.

Na Nam-Soo, a programming director suspended for exposing a corrupt national assembly member, is assigned to investigate what happened to the hospital, which recently burned down. He begins gathering clues and learns of Soo-Ah’s possible connection to the case.

Nam-Soo discovers a notebook belonging to Soo-Ah, but cannot find any verified information about the fire itself. Deciding the truth must come from Soo-Ah, he resolves to seek her out directly.

Nam-Soo visits Soo-Ah in prison to coax out the truth, but she remains emotionally distressed and uncooperative, shielding herself and others from the full story. Her reluctance deepens the mystery surrounding the hospital.

During a visit to the burned hospital with his crew, Nam-Soo encounters a heavily burned Dong-sik and questions him about Soo-Ah’s diary. Dong-sik's cautious replies push Nam-Soo to dig deeper into the diary’s meaning and the hospital’s true purpose.

Nam-Soo learns that the hospital was a front for an organ trafficking and disappearance scheme, founded by police commissioner Kang Byung-joo, with Jang Hyung-sik as his protégé. The operation exploited loopholes in the law to disappear enemies or undesirables.

Nam-Soo broadcasts the hospital’s corruption to gain public support and pressure Soo-Ah to speak openly. Soo-Ah comes forward to confess, revealing her connection to Byung-joo, while Nam-Soo presents incriminating documents that expose the scheme. The fallout leads to public outrage and official scrutiny, and Byung-joo is said to have committed suicide following the hospital’s destruction.

In a final revelation, Nam-Soo learns that Soo-Ah was not the person in the hospital at all; the diary in Nam-Soo’s hand belongs to Dong-sik, and the one who was rescued in the hospital was actually Soo-Ah, while Woo-Jin is Soo-Ah’s late father. Hyung-sik killed Soo-Ah’s mother, and Soo-Ah killed Byung-joo in revenge. Nam-Soo chooses to bury these secrets so that Soo-Ah can live a normal life.