In 2019, a local boy's disappearance stokes fear in the residents of Winden, a small German town with a strange and tragic history.

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

It's 1986, and Ulrich's brother, Mads, has been missing for a month. Confusion reigns as past and present intertwine.

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.

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.

Armed with a plan to prevent the apocalypse, Jonas travels to 2019. During the Nielsens' anniversary party, Ulrich sneaks off with Hannah.