Around the Christmas of 1985, not long after Mads's twelfth birthday, he and his brother got into a fight. One thing led to another, and Mads went crashing through the glass coffee table. Although he bled profusely, he ended up with just a small cut on his chin, which became a scar. His mother Jana reflects on this memory in 2019, remarking that that's how Mads and Ulrich were: One minute they hated each other, and the next they were best friends.
At the age of twelve, Mads walks back home through the forest after walking Regina Tiedemann to her house. He did it knowing she is afraid of the woods because his brother Ulrich and Ulrich's girlfriend Katharina Albers tied her to a tree and left her there in the night over the summer. He is taken by Helge Doppler, who is working on Noah's behalf.
Regina is documented as the last person to see him alive in the police investigation.
Mads is never found in his own time again. Tronte suggests that they place a grave for Mads, to get closure. Jana, however, will never get closure—there's no body in the grave.
After the mock burial, the Nielsens hold a wake at their house. Hermann Albers is there, who commends the parents for doing what they did, to get closure. Jana makes a mock toast to closure. She then urges Tronte to tell the crowd where he was the night that Mads disappeared. When he says nothing, she says that he was "screwing Claudia Tiedemann." When he feigns ignorance, she reveals the collection of newspaper clippings and other research by him that she found, dumping them out of her purse onto the floor.
Mads appears in the bunker in 2019 before Peter Doppler. Peter calls Tronte, who quickly arrives. They are found by an elderly and long-missing Claudia Tiedemann, who tells them they must move the body to the place it must be found.
Mads's corpse is found in the forest by the police. It is taken into custody and his belongings are catalogued. His body is found with a 1986 pfennig coin on a red string around his neck. This same coin and string is found on the other bodies that Noah sends through time. He also has a Walkman that contains a cassette with Nena's song Irgendwie, Irgendwo, Irgendwann (Somehow, someplace, sometime). His body is mutilated, with his eyes burned out and inner ear ruptured, which is consistent with Noah's other victims.
Ulrich deduces that the body of a young boy found in the forest on the morning of November 5, 2019, the night after his son Mikkel goes missing, is the young Mads Nielsen who went missing thirty-three years prior.