On Christmas Eve, 1899, Edward Newgate [Sturgess] arrives at the imposing gates of Stonehearst Mental Asylum, eager to be granted an apprenticeship with the superintendent.
Delighted to share his knowledge and philosophy, Dr. Lamb [Kingsley] agrees and immediately takes Edward on a tour of the asylum, proudly introducing his staff and the troubled patients in his care, including the hauntingly beautiful Eliza Graves [Beckinsale] – a captivating woman whose violent aversion to intimacy has ensured her permanent residence at Stonehearst.
As the days pass, Edward observes Lamb’s modern methods. The “medieval” practices so favored by his predecessor, Dr. Salt [Caine], have been abolished and his patients are never sedated, segregated or locked up. Instead, they are celebrated as individuals in their natural, unadulterated state of lunacy. Lamb’s vision is to build an enlightened society within the walls of his establishment, where the patients are respected and mingle with the staff as equals.
However, one night Edward notices a strange thumping noise coming from the vent in his sleeping quarters. Intrigued, he follows the sound down into the dark asylum cellar. At first unsure of his surroundings, he is astonished to discover Dr. Salt, locked behind bars with Matron Pike and their orderlies. As Dr. Salt tells of Lamb’s deadly past, a dawning horror engulfs Edward and he realizes the lunatics have taken over the asylum.
With fresh awareness, Edward can only watch as Lamb’s lawless utopia starts to crumble; there is no heat, little food, and his grand experiment is reaching terrifying new levels of fanaticism. Knowing he must intervene before it is too late, Edward struggles to find a way to save Lamb’s prisoners and restore order at Stonehearst, but his efforts will be futile without the love and affection of the mysterious Eliza Graves.