In August 1984, Josef Fritzl lured his eighteen-year-old daughter Elisabeth into a specially built cellar beneath the family home in Amstetten, Austria, and kept her locked there for the next twenty-four years. He raped her repeatedly, fathered seven children with her, and told his wife and the outside world that Elisabeth had run off to join a cult. Three of the children were raised upstairs as foundlings left on the doorstep; three stayed underground with their mother, never seeing daylight until the youngest fell seriously ill in 2008 and hospital staff grew suspicious enough to call police. This film goes through the case file: the concealed door disguised as a shelving unit, the soundproofing, the neighbors who noticed nothing for over two decades in an ordinary-looking house on an ordinary street. It weighs what the discovery exposed about how thoroughly a crime can hide inside a family, and what it took for investigators to finally get through that door.