A powerful storm surrounds the island of Heligoland, isolating it from the mainland. Amid this chaos, Linda, a 24-year-old cartoonist, is on the island temporarily, escaping the threats posed by her ex-boyfriend Danny who persistently stalks her. In her desperate attempt to evade him, she stumbles upon a corpse on the beach after falling down an embankment.
At the same time, Prof. Dr. Paul Herzfeld, portrayed by Moritz Bleibtreu, is conducting an autopsy at the Charité University Hospital in Berlin when he discovers a mysterious capsule lodged inside the head of a female corpse, whose jaw is missing. Inside the capsule is a slip of paper with the phone number of his estranged daughter, Hannah, who is only 17 years old. Heartbreakingly, he soon realizes she has been kidnapped. An ominous voice instructs him not to contact the police if he wants to spare Hannah’s life, promising to send more information through a man named Erik.
While Linda stands near the corpse on Heligoland, the phone belonging to the deceased suddenly rings. She answers and speaks to Herzfeld, who instructs her to find Ender Müller, his friend and the caretaker at the local hospital, so they can transport the body together. As Herzfeld begins his frantic journey to find his daughter, accompanied by his intern, Ingolf von Appen (played by Enno Hesse), the story intensifies with disturbing flashbacks of Hannah being subjected to horrific abuse at the hands of the kidnapper, Jan Erik Sadler, which includes the mental torment of being coerced into suicide.
Linda, who is both disgusted and a vegetarian, hesitates at the task of conducting a thorough examination of the corpse, which Herzfeld has guided her to perform. As the exchange of information continues, and after discussing the chilling situation with Herzfeld regarding her ex-boyfriend, she resolves to move forward with the necropsy. To her shock, she discovers a Kinder Surprise capsule lodged in the throat of the deceased, which is accompanied by a photograph of Judge Friederike Töven (Klara Höfels)—known for giving a lenient sentence to Sadler after he preyed upon a tragic young victim.
Driven by her commitment to uncover the truth, Linda, alongside Ender, breaks into Judge Töven's residence, where they discover another woman's corpse. At the same time, Herzfeld and Ingolf discover alarming evidence linking Sadler to the tragic fates of both of their daughters. After much peril, including Ingolf's near-fatal fall into a frozen lake, the plot weaves a deeper narrative of vengeance and justice, highlighting the tragic aftermath of crime and the lengths one will go to seek retribution.
The tension escalates dramatically when Ender, trying to ensure the clinic's power supply, returns to the autopsy room severely injured. Linda uncovers horrifying evidence that leads them to geo-coordinates tied to the scenes of violence committed against the girls. Heart-wrenchingly, Herzfeld discovers a video revealing the desperate actions of Marinek and Schwintowski, who felt pushed to avenge the loss of their daughters after the failure of the judicial system.
As Herzfeld orchestrates a rescue plan using a calculated car accident to alert authorities, he arrives just in time to save Linda and Ender from yet another attack by Sadler. They come to realize that Schwintowski had also fallen victim to Sadler, who had orchestrated events to stage his own death. The connections intensify, taking them to the foreboding Nazi-era bunkers beneath the lighthouse, where they come face to face with the realities of Hannah's abduction.
In a stirring climax, Herzfeld frees his daughter from a ghastly scenario involving harrowing recordings of past abductions, dispatching a chilling reminder of justice gone awry. Before their departure on the helicopter, Herzfeld expresses his gratitude to Linda for her assistance. However, the nightmare isn't over; as they fly above the turbulent waters, Sadler makes a shocking move, attacking the group within the helicopter. In a gripping moment of desperation and instinct, Herzfeld must confront his deepest fears and make an irrevocable decision to secure his daughter's safety, culminating in a heart-stopping conclusion where he cuts Sadler's fingers, leading to his fatal fall.
This intense journey abounds with moral complexity, as each character confronts their torment and the weight of unforeseen revenge—transforming the island into a haunting landscape of horror, grief, and unexpected heroism.