George Grieves (Thomas Cavanaugh) has just turned forty and finds himself at Mt Abaddon Hospital for a routine colonoscopy. After some scary stories from his friends about medical mishaps, George begins to get worried and his worst fears are about to come true. His physician, Dr. Sharazi (Cas Anvar) doesn’t help ease the patient’s mind, and things go from bad to worse. When George’s chart gets mixed up with another patient, he has the wrong surgical procedure. His wounds begin to fester and become infected with flesh-eating bacteria, his family is being torn apart, and a maniacal nurse named Mandingo (Lawrence Hilton-Jacobs) seems bound and determined to ensure George Grieves never makes it out of Mt. Abaddon alive.