Based on true events, the film follows Sarah, a spirited teenage girl who is looking forward to her 18th birthday so she can leave her controlling father Don (Judd Nelson). But before she can blow out the candles, Don locks her up in the basement of their home and her world becomes very dark. As Don tries to convince his wife, Irene (Joely Fisher), that Sarah is running away, he would sneak into the basement to visit her, torture and rape her while Irene and her sister, Amy (Emily Topper), continue to live upstairs. Over time, Sarah gave birth to several children, alone in the basement. Don ends up raising their youngest son, leaving him on the doorstep, where Irene finds him and a note from Sarah saying it is her son and she can’t take care of him, and Irene eventually accepts Don’s version of events about Sarah. After decades of captivity, Sarah finally escapes and her family learns the devastating truth about what had been happening right under their feet for 20 years.