"Dark" is a German science fiction thriller series that intricately weaves time travel, family secrets, and interconnected destinies across multiple timelines. Set in the fictional town of Winden, the story begins in 2019 with the disappearance of a young boy, Mikkel Nielsen, which unravels a complex web of events spanning several decades. The narrative explores the lives of four families—the Nielsens, the Dopplers, the Tiedemanns, and the Kahnwalds—whose fates are deeply intertwined.

The central mystery revolves around a cave near Winden that serves as a portal for time travel, connecting key years: 1953, 1986, 2019, and later 2052 and 1921. As the characters investigate Mikkel's disappearance, they uncover a cyclical pattern of events driven by a secretive time-traveling organization. Jonas Kahnwald, a teenage boy grieving his father's suicide, becomes a pivotal figure in the story. He discovers that his father, Michael, was once Mikkel, a boy who traveled back in time from 2019 to 1986 and grew up in the past. This revelation ties Jonas to the broader timeline and positions him as a key player in the struggle to break the cycle of destruction.

The narrative introduces a dual timeline involving two versions of Jonas: one who seeks to prevent the apocalypse and another, an older version, who works to ensure it occurs. The older Jonas, known as "The Stranger," is revealed to be manipulated by Claudia Tiedemann, a former power plant director who has spent decades navigating the timelines to alter the course of events. Claudia's actions are driven by her knowledge of the time loop and her desire to create a new reality free from the constraints of determinism.

The series delves into themes of fate, free will, and the consequences of human actions. Characters such as Ulrich Nielsen, a police officer desperate to save his son, and Charlotte Doppler, a detective investigating the disappearances, grapple with their roles in the unfolding events. The intricate plot reveals that many characters are unknowingly connected across generations, with their actions in one timeline influencing outcomes in another.

As the story progresses, the existence of a parallel world is revealed, introducing alternate versions of familiar characters and further complicating the timeline. The final season focuses on the conflict between the two worlds and the ultimate resolution of the time loop. The series concludes with a resolution that ties together the fates of the characters and the timelines, emphasizing the cyclical nature of time and the possibility of breaking free from predetermined paths.