The small German town of Winden is shaken by the disappearance of a teenage boy. While the townsfolk are occupied with secrets of their own, at nightfall a group of teenagers attempts to recover something the missing boy may have left behind.

When a grim discovery leaves the police baffled, Ulrich seeks a search warrant for the power plant. A mysterious stranger checks into the hotel.

Bizarre occurrences give Charlotte a sense of déjà vu, and she suspects Peter is hiding something. Franziska snaps when Magnus confronts her.

Hannah takes her obsession with Ulrich too far. The stranger asks Regina to deliver an important package. Martha is torn between Jonas and Bartosz.

Ulrich looks to the past for answers and dredges up disturbing family secrets. Armed with new tools, Jonas probes the cave's murky depths.

Ulrich questions a frail and frightened Helge in the nursing home. Jonas searches for Mikkel, but the stranger warns him about meddling with the past.

In 1953, the disfigured bodies of two boys are exhumed at a construction site, the future location of Winden's nuclear power plant.

Ulrich runs afoul of the law, Helge tries to dodge Egon Tiedemann, Claudia harnesses the cave's powers, and Katharina lashes out at Hannah.

Peter gets a shock. Jonas learns the truth about his family, but there are more surprises still to come. Helge makes a sacrifice.