Antidote

Sharyn Berkley is rushed to the hospital by her husband after severe stomach pain and is diagnosed with acute appendicitis requiring emergency surgery. After waking from the procedure she is greeted by Dr. Aaron Hellenbach, who hints at unconventional healing methods used by the facility. She notices the lower abdominal incision is nearly fully healed, which unsettles her.

Sharyn questions the healing she received and learns that the facility employs unconventional methods. She tries to leave her room and briefly encounters Rizzo before hospital staff sedate her again. The sense that something is not right is reinforced by the facility's secrecy.

Sharyn is confined to her room and starts exchanging notes with her neighbor Everett through a hole in the wall. She witnesses a man with bleeding eyes being led down the hall and later hears Everett being attacked in his own room, heightening the sense of danger inside the facility.

Sharyn meets Cassandra Franklin, Rizzo, Marjorie, Lester, and Everett, learning that the place is an experimental facility. Cassandra recounts that she had been burned alive, and Everett notes that others here have troubling histories. The group learns the facility keeps dangerous secrets.

Rizzo is chosen for the 'Indexing' procedure and reveals that he has already suffered grievous injuries, including impalement. Dr. Hellenbach administers a healing serum to him, hinting at the bizarre, self-inflicted nature of the facility's methods.

Dr. Hellenbach questions Sharyn about her past, including her ex-boyfriend Nico. When Sharyn cannot use the phone, she roams the halls and discovers a piano room with a noose. As punishment for rule-breaking, her left leg is amputated and then reattached, signaling the brutal regime at the facility.

Sharyn tries to escape again but fails. Everett tells her that if they cooperate, they will be released in three months; when Sharyn reveals she saw Nico alive, Everett's tongue is cut out again, showing the cost of defying the system.

Sharyn and Cassandra plan an escape, stealing Dr. Hellenbach's keys and discovering a facility map. They evade the med-room staff and narrowly avoid capture, but Cassandra's suicide attempt buys Sharyn time to flee.

During their attempt to hide, Rizzo gropes and kisses Sharyn, prompting her to violently retaliate by ripping out his testicles. She then continues her escape, solidifying her determination to break free from the facility.

Sharyn finally reaches the outside exit and begins to flee, but an alarm sounds and staff pursue her. She is eventually brought back to the facility and later experiences a hanging in the piano room, waking with questions about why Dr. Hellenbach keeps healing rather than killing.

Sharyn confronts Everett and learns about the accident and injuries that brought him to the facility, including the broken ribs and neck. She also probes whether he has done terrible deeds, hinting at shared guilt that ties them to the place.

Sharyn discovers Cassandra alive in her room and Cassandra explains fierce past acts, including burning a mink farm and killing sleeping farmers. Cassandra claims that the only way out is death, arguing that they are already in Hell, a place of perpetual torment.

Sharyn confronts Hellenbach, who is reading Dante's Inferno. He reveals that everyone in the facility is a patient and that Hell is a cycle of endless healing and torment. He has been in Hell since 1969, explaining the institution's true purpose.

Nico appears and helps Sharyn escape, but they are confronted by Hellenbach. Nico overpowers the doctor and the pair reach the edge of a lava-filled cliff; a path across the lava forms and Sharyn crosses, though Nico cannot follow.

Sharyn awakens in a hospital bed after a medically induced coma and learns she was clinically dead for about 15 seconds. Her husband and daughter come to her; she later searches online and finds an article confirming Hellenbach's death in 1969, as well as Cassandra's death, and ends by visiting Nico's grave.