The full story
Jonah's family has possessed Victor, Stacey and Tina, and is keeping Karolina, Chase and Janet Stein in a simulation where each lives out their greatest desire. Alex and Nico get inside, and Chase and Karolina escape, but Janet Stein stays behind so they can. Catherine, in prison for Darius's murder, is killed by inmates hired by Darius's widow, Tamar, and Alex turns out to be possessed by one of Jonah's family too, the Magistrate's son. Leslie gives birth to a daughter, Elle. Xavin learns that her prophecy meant raising Elle, takes her into space, and Nico uses the Staff of One to make Jonah's family vanish.
The Runaways wake in the Dark Dimension and get out, but without Alex, and find six months have passed. Morgan le Fay, the sorceress Nico has been seeing in visions, has taken over the tech company WIZARD and is giving out free Corvus phones that turn their users violent. She offers to train Nico, and Nico accepts to save Alex and breaks up with Karolina. Morgan kills Robert Minoru. Then Tandy Bowen and Tyrone Johnson arrive from New Orleans and take Nico and her friends into the Dark Dimension, a ruined Los Angeles, where Alex is being held. Alex gives in and kills Catherine there, and that frees them all. As they leave, Tandy sees that Alex wants his friends' powers.
Morgan recruits Molly into her coven, and the Pride reunites to rescue her. Morgan plans to merge the Dark Dimension with Earth and use the phones to build an army. Janet Stein knocks out Los Angeles's phone service, and Tina banishes Morgan back to the Dark Dimension, but Gert is mortally wounded and dies in Chase's arms.
Three years later the friends have gone their separate ways, until an evil Alex from 2028 arrives to kill them, chased by the Chase of his own time. The future Runaways travel back to the battle with Morgan and save Gert, and future Chase dies doing it. In the final scene Alex finds a note from his future self telling him to hide someone called Mancha and to kill Nico. He pockets it and joins his friends for breakfast.