Dark is a very complicated series. So if you have seen the show, and you are waiting for season 3, this will provide you with a recap. If you haven't and still read this, please get to somewhere you can sit down and have an emotional support animal nearby.
Also, if you are not sober, I must warn you, this information might take you for a spin.
There are essentially four families at the core of this series. Dark follows the Kahnwalds, Nielsens, Tiedemanns, and Dopplers, all of whom are in some way or the other connected by a 33-year-cycle of trauma, primarily between 2019-2020, 1986-1987, and 1953-1954.
Now time travel is made possible in the series by something called a God particle. It is a swirling mass of black matter created in 2020 at Winden's nuclear power plant. When stabilized, it acts like a wormhole, allowing anyone and anything to can travel through time.
Now speaking of the characters...
Jonas Kahnwald is a teenager in the pilot episode. Claudia is an adult woman who has harnessed the power of time travel and is guiding Jonas. Martha is a teenager who Jonas loves — but their relationship is complicated.
Mostly because they have a whole Jon-Dany thing going on. They are technically aunt and nephew, because Jonas' father is Martha's younger brother who got stuck in the past.
Martha's little brother, Mikkel, time travelled to 1986 (in the pilot episode) and got stuck there. So he changed his name to Michael, grew up, got married, and eventually had a child- Jonas.
Now Mikkel died by suicide just a few months before his younger self goes missing in 2019. BTW, only reason why Mikkel/Michael ever died was because Jonas came and told him about his death, giving him the idea.
I told ya, it's trippy AF. Now, let's get on with it.
There are multiple devices that have been built and changed hands over the years to help the loop of time travel. One of those is a tunnel located in a cave in Winden, wacting as a portal between 1953, 1986, and 2019.
There is a doorway to the cave's passage, which was created by the Sic Mundus group at an unknown time.
Sic Mundus is a secret society of time travellers in Winden who are waging a war on God and time.
Now Jonas, who is in 2053 at the start of the second season, finds the God Particle in the plant's ruins and travels to 1921, where he is introduced to Adam, the leader of Sic Mundus.
During Adam and Jonas' conversation, Adam reveals he is actually Jonas, just 66 years in the future.
Remember Claudia, from earlier in the article, who teaches Jonas about time travel? Yeah, well, it turns out Adam (older Jonas) and she don't really get along. They are on opposite sides of a war. So she taught Jonas how to time travel so that he can go back to her younger self and takedown Adam, his older self, who is trying to destroy the world and start a new one.
So, throughout season one and two, Jonas works with either Adam or Claudia to alter or change the cycle of events that keeps happening. We still have no idea how Jonas transformed into Adam, mentally or physically.
If you are still following this, I'll do you a favour and keep it short from here on.
Noah was one of the people who worked under Adam(leader of Sic Mundus). Through his ability to time travel, Noah meets Elisabeth when they were both young. They grew into adults between the year 2019 and 2053, and had baby Charlotte.
But someone took Charlotte back in time and hid her there, so she grew up throughout the '80s and had a family of her own, eventually giving birth to Elisabeth.
So, Noah is the father of Charlotte, and Charlotte's own daughter (Elisabeth) is her mother. In season two, Noah revealed to the adult Charlotte that he was her father.
Now, Charlotte's husband is Peter Doppler, who learnt the truth about time travel and the bunker that held Noah's captives.
After which, Peter and Charlotte started learning more about time travel from a notebook which had detailed information about the three time cycles and time travel.
Going back to Jonas' story... The day the apocalypse is 27 June 2020, and there are two versions of Jonas at different periods in time trying to stop it from happening.
The younger Jonas is primarily with Claudia. The middle-aged Jonas talks to his own mother Hannah and Mikkel's mother Katharina.
Just before the apocalypse (2020), a young Noah finds middle-aged Jonas and gives him a letter.
Noah says that letter was written by Martha. We don't get to read it but it visibly disturbs Jonas. Noah tells this Jonas to save Martha and their friends and allow the cycle to continue so that Martha can live. Middle-aged Jonas brings Martha to the bunker to protect her.