The high school teacher Mathias Mahnke is sentenced to life in prison for the murder of his student Annika. When Mahnke is released from prison after 17 years, he is determined to prove his innocence, especially for the sake of his son Sören. With the help of a journalist, the former teacher struggles to shed light on the mysterious murder case in a moorland area of the Lüneburg Heath. Who killed Annika? What happened on the shores of the Bottomless Lake? What are Annika's former classmates hiding? The investigation stirs up the small town of Walsrode and leads to further crimes. The murder of Annika haunts those involved from the tranquil Löns landscape in the heath to Timmendorfer Strand.