The film is based on the true story of Natascha Kampusch, a 10-year-old girl and her eight-year ordeal being kidnapped by Wolfgang Přiklopil.

Northern Irish actress Antonia Campbell-Hughes portrays Kampusch,[1] while Thure Lindhardt plays Přiklopil.

Despite being erratic, odd and tyrannical with Natascha, in public Wolfgang is socially awkward and very lonely, with his only contact being his mother, who occasionally comes to visit and bring meals to him.

When Wolfgang's mother is pleasantly surprised to find a girl's hair on his sweater, he shaves Natascha to avoid raising further suspicion.

Relaxing in the finished bedroom, Wolfgang explains that he did not pick Natascha at random, but rather became fascinated with her at a store and spent the following months building the cellar and planning her kidnapping.

In late 2012, concerns arose about Campbell-Hughes' drastic weight loss for the film, but she stated in an interview in the Evening Standard that she wanted "to suffer as much as she – Kampusch – did".

[3] She also noted that she received a torn Achilles tendon, a broken toe, a fractured rib, and various cuts and bruises, due to the film set being similar to the dungeon in which Kampusch was placed.