Claus Jansen experiences the inconceivable: his 12-year old son disappears without trace from his boarding school and is then found murdered. As the police don't seem all that committed to their enquiries, the father sets out to try and find the sex offender and is successful, albeit many years later. The film is based on the true story of Ulrich Jahr, whose son was the first victim of the "man in the mask" in 1992. After murdering three boys and abusing dozens of others, he was caught in 2011. One of the most disturbing cases in recent German criminal history.