In 1921, a young man named Noah and another man built the place to be the door. Another man trust the Noah very well.

Noah kills his companion on suspicions. The younger Noah is guided by his older self, a member of a society of time travellers called Sic Mundus led by the disfigured and mysterious Adam. 

Adam tells adult Noah to retrieve Claudia's diary in preparation for an "apocalypse" that will occur on 27 June 2020.

On 21 June 2020, six days before the apocalypse, an investigator, Clausen, arrives to help Winden's police investigate the disappearances, which now include Helge, Jonas, and Ulrich. 

Katharina searches the cave for answers. Martha breaks up with Bartosz, who is now working with Noah. 

The adult Jonas from the future reveals his identity to Hannah. Aleksander has a truck of radioactive waste moved into the power plant.

In 2053, the teenage Jonas is stuck in post-apocalyptic Winden. He is monitored by the now adult Elisabeth, who survived the apocalypse and now leads a group of survivors.

She forbids entry to the power plant under penalty of death. Jonas enters the Dead Zone nonetheless and finds a large, floating amorphous black blob inside.

In 1987, Mikkel struggles to adapt to life with Ines. Old Claudia visits her younger self, giving her coordinates of a time machine buried in her backyard.

Egon has retired and begun to doubt his actions regarding the dead children's bodies in 1953. He interviews Helge and visit an elderly Ulrich. Ulrich rebuffs Egon for his naivety.

In 2020, Clausen and Charlotte interview Regina, who is slowly dying from cancer. She discusses the Stranger who left his belongings at her hotel, which included pages from Tannhaus' book.

The newfound evidence makes Charlotte, who was raised by Tannhaus, question her origins. Adult Jonas informs Hannah about time travel and takes her to 1987, where they see Mikkel in Ines' house.

In 2053, Jonas learns via recordings by Claudia about the "God Particle", the blob in the reactor usable as a portal for time travel. He is caught by Elisabeth stealing fuel for the portal. 

But she imprisons him instead. Elisabeth's interpreter Silja, curious, frees Jonas. They enter the Dead Zone and access the God Particle. Jonas heads inside, leaving Silja behind.

In 1954, a young and disfigured Helge returns but refuses to talk to anyone but Noah, with whom he spent the last seven months in 1987 building a new time machine. 

Doris cheats on her husband, Egon, with Agnes. Elderly Claudia later meets with Agnes, a former member of Sic Mundus. Agnes meets with Noah, her brother, and discloses the missing pages' location. 

Claudia delivers Tannhaus' book to him, then apologizes to her father's younger self, to his confusion. Claudia encounters Noah in the forest, who kills her. 

Noah retrieves the missing pages and is dismayed by his findings. He lies to Adam about finding the pages. Egon unsuccessfully interviews Helge and visits a catatonic Ulrich in jail.

In 1987, Egon visits the older Ulrich at the asylum. Ulrich tells Egon his identity after interviewing Ines, Egon shows older Ulrich a photo of Mikkel. Ulrich attacks Egon and is restrained. 

Egon visits Claudia at work to tell her he has cancer, and then she uses the time machine she found to travel to 2020; she cries upon seeing a dying Regina at her home.

An injured Jonas finds himself in Winden in the year 1921. He then tries to return to 2020 through the portal, but it yet to be built. Noah escorts him to meet Adam, who is himself elderly Jonas.

In 2020, adult Jonas and Hannah meet Charlotte and Peter at the bunker and they discuss the existence of time travel, which they also reveal to a sceptical Katharina.

The 1987 version of Claudia visits Winden's public library, where she discovers a report on Egon's death; she then travels back to 1987.

Clausen interviews Aleksander, who reveals his original surname – Köhler – before he married Regina. 

Martha, Magnus, Franziska, and Elisabeth visit the cave, where they find Bartosz carrying the time machine. The kids take the time machine and leave Bartosz tied up in the cave.

Katharina searches the school archives for the class photo of 1987 and identifies Mikkel, confirming Jonas' claims.

In 2053, Silja walks into the power plant, where she is confronted by the adult Elisabeth at gunpoint. They have a heated conversation in which Elisabeth admits her knowledge of the God Particle.

In 1921, Adam speaks with Jonas, who is dismayed by the callous person he is to become. Adam shows Jonas a God Particle that will take him to any time he wants. 

Jonas decides to go to the day before Michael kills himself to convince him not to do it.  As he thinks this is the only way he can stop the life chain. 

In 1987, Claudia invites her father Egon to move in with her in hopes of preventing his impending death. But Egon don't wants to go with Claudia as he feels he is on his deathbed.

Ulrich escapes the psychiatric ward to visit Mikkel at the Kahnwald house. After a conversation, Mikkel realises that the old man is actually his father.

Ulrich tries to take Mikkel to the cave but is apprehended by the police. Ulrich blames Egon for his condition.

In 2020, Katharina attempts to explain to Magnus and Martha what she discovered but is rebuffed for her distant behaviour. Katharina then approaches Hannah for help understanding time travel.

Adult Jonas goes to the Doppler house to help Charlotte, who explains that Tannhaus is not her real grandfather and that she never learned her parents' identities. 

Magnus, Martha, Franziska, and Elisabeth return to the caves, where Bartosz explains the time machine before taking them to 1987.

Noah visits Charlotte at Tannhaus's workshop, revealing to her that she is his daughter. Charlotte not believing him and he shows her an old photo of Noah holding a small baby Charlotte.

Jonas travels back to 20 June 2019 to stop Michael from killing himself. Jonas' 2019 self goes to the beach with Martha, Bartosz, and Magnus.

Michael has a tense encounter with his child self; Charlotte and Peter struggle in the wake of Peter's affair; Aleksander fears his past will catch up to him. 

2020 Jonas shares a kiss with Martha. 2019 Jonas and Hannah arrive at the Nielsen home on Ulrich and Katharina's anniversary, where Jonas has sex with Martha and Ulrich starts his affair with Hannah.

2020 Jonas reconciles with his father as he tries to convince him to not kill himself. However, Michael reveals that Jonas was the one who led Mikkel into the portal in the first place.

 After reading his suicide note, Michael suggests Jonas is really there to inform Michael of what he must do.

The elderly Claudia arrives at the house and convinces them that Michael must die and Mikkel must travel to the past so Jonas can be conceived.

In 1921, two members of Sic Mundus—older versions of Magnus and Franziska—share concerns with Adam about his next move.

In 1954, Egon learns from the coroner that Claudia, discovered shot to death, had unusual amounts of radiation exposure.

They theorize that she kidnapped Helge, but Helge says "he" told her about Claudia, the White Devil.

Hannah travels to 1954 and asks to see Ulrich at the asylum. Ulrich promises he will leave Katharina for her if she helps him get out, but she does not believe him and coldly walks away.

In 1987, Claudia tries to prevent the death of her father. Egon deduces that she knows about time travel and is selfishly using the caves for her own gain. 

They struggle for the telephone and he falls and hits his head. As he dies, Egon tells her she is the White Devil. 2020 Jonas arrives and tells Claudia they still may be able to change the events.

In 2020, Martha meets adult Jonas. 

Clausen confronts Aleksander about his background and informs him that in 1986 his own brother disappeared and that his name was Aleksander Köhler.

Clausen shows him an anonymous note explaining that the answers to his brother's disappearance could be found in Winden. Aleksander says nothing.

In 1921, Noah tries to kill Adam for lying to him, but his gun fails to fire. Adam says he cannot be killed because that is "not his fate". 

He then explains that Elisabeth will become young Noah's wife and therefore Charlotte's mother, after which Agnes appears and kills Noah.

In 2020, young Jonas explains to Claudia that her elder self taught him how to save the world, whereas Adam wants to destroy it. 

Charlotte learns of the radioactive waste buried in the power plant; she believes that Clausen will provoke the apocalypse.

Before the apocalypse, Peter, Elisabeth, 1987 Claudia, Regina, and teen Noah take shelter in the bunker.

Young Jonas and Martha reunite but are interrupted by Adam, who shoots Martha. In the power plant, Clausen opens the drums containing rocks soiled with dark matter.

In the power plant, Clausen opens the drums containing rocks soiled with dark matter.

In 2053, Elisabeth activates the machine, simultaneously as Magnus and Franziska do so in 1921. 

Katharina enters the cave and opens the gate, opening a portal linking Elisabeth to Charlotte in 2020.

Adult Jonas takes Bartosz, Magnus, and Franziska to an unknown time, while young Jonas meets another version of Martha who says she is not from another time, but from another world.