A seemingly ordinary assignment turns into a life-threatening situation for private detective Johanna Schiller: While investigating marital infidelity, she witnesses a planned double murder. Shortly thereafter, she discovers a body in the trunk of her car - the hunter Johanna has become the hunted. In a panic, she flees from her hometown of Siegburg upstream along the Sieg River to the Siegerland, but her pursuers are hot on her trail...