Jonas meets an ominous figure; as the kids comb the cave for answers, the adults gather in the bunker to share what they know about the travelers.

In 1987, Ulrich seizes an opportunity; the kids return to the cave with the time machine; Jonas learns of a loophole that could change the future.

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

Martha meets the Stranger and learns his true identity; Claudia tries to prevent Egon's death in 1987; Hannah travels to see Ulrich in 1954.

On the day of the apocalypse, Clausen executes a search warrant at the power plant as Jonas and Claudia use the time machine to connect the past and the future.

In 2019, Jonas emerges from the cave into a strange but familiar world in which the town of Winden is reeling from the recent disappearance of a young boy.

Martha travels to 1888 to warn her friends about the 2020 disaster; Winden residents -- past and present -- search for their missing loved ones.

Charlotte and Ulrich try to figure out what happened in the bunker; in different times and worlds, Jonas and Martha strive to gain each other's trust.

Martha and Jonas travel to 2052 and get a glimpse of a grim future; in 1954, two townspeople go missing; Hannah receives surprising news.

In 2020, a visitor delivers a warning to Claudia; Jonas questions Eva's motives the day before the apocalypse.

Adam holds Martha captive in 2020; a frantic Martha begs Bartosz for his help on the day of the apocalypse.