«اتاق» داستان مادری فداکار (که در فیلم “ما” نامیده می شود) و فرزند کوچکش جک را روایت می کند. جکِ پنج ساله شور و شوق کودکانه ای دارد ، اما به هیچ عنوان اطلاعاتی از دنیای پیرامون خود ندارد. وی در اتاقی محبوس شده و فکر می کند که دنیا نیز همانند آنچه که می بیند وجود دارد و ابداً نمی تواند ابعاد بزرگتری داشته باشد. “ما” که خود دچار انواع و اقسام بیماری های روحی و روانی شده ، به سختی سعی می کند تا اجازه ندهد روح جک نیز مانند خودش ، پوسیده و نابود شود.
Five year old Jack's entire life consists of his Ma and whatever he has where they live, Room. Room is an approximate ten by ten by ten foot cubed structure, out of which he's never been. Seven years ago, Ma - Joy Newsome, the daughter of Bob and Nancy Newsome - was abducted by "Old Nick", the man who is keeping them captive in Room, which is really a tool shed in his back yard, the shed's only door secured by a number coded keypad, the code which only Old Nick knows. They are dependent on Old Nick for their basic necessities, such as food, water, clothes and utilities. Whenever Old Nick does stay for extended visits in Room, Ma will not let Jack see him or visa versa, Jack who is supposed to hide "asleep" in the wardrobe. Old Nick has no desire to see his biological offspring anyway. To shield him from anything that is happening to them, Ma has told Jack that the two of them and Old Nick are the only real things, and that what Jack reads about in books or sees on television are all not real. Jack believes that Old Nick gets their food by magic from television. The only exposure they have to natural light is a skylight at the top of Room, out of which they can only see sky. Joy knows she can't kill Old Nick because they would still be locked in Room. Joy tried to escape only once before Jack was born, that attempt which failed and which resulted in her not having tried again... until now. She has made this decision to try to escape partly due to Jack's age where he can now understand things better, and an incident which showed Joy what were to happen if something truly did happen to Old Nick with them locked inside. If they are able to escape, not only would Jack be required to adjust to a life and a world he may have no comprehension about, but Joy may find that the outside world is much more difficult to adjust to than she imagines, and not only because of the changes to outside in seven years.