After the events of "Doomsday" revealed the PRIDE's dig at the site of their future school could result in the destruction of Los Angeles, the kids are confronted by their parents at the massive hole in the ground.
"Hostile" kicks off with the kids using their powers, and Gert's pet dinosaur joining in on the fun. Dale Yorkes whips out a tranquilizer gun for his creation, but Gert withdraws the darts. In the standoff, Chase and Karolina blast their folks with Fistigons and glowy powers respectively.
But when Molly tries to help and toss a barrel or two their way, Jonah shows up and uses some Karolina-like glow blasts of his own. He angrily tosses Tina Minoru's staff aside, and as the parents plead for mercy for their children he ignores and blasts them back anyways.
The children stand tall, resolute, and unite before the PRIDE once again, causing a standoff between Karolina and the man she doesn't know is her real father. She tells her friends to run away so they can escape, promising to hold PRIDE off. They get away as a huge blast of light engulfs the construction site, all while Darius watches from the shadows.
Nico wants to go back to retrieve Karolina, but the others want to escape. But the light also acted as an EMP pulse, frying all electronics -- including Gert's car. Ignoring Alex's advice to be smart, Nico goes back to the site to see Jonah and Karolina missing. With the parents looking for them, they take off into the streets as the sun rises, hiding Old Lace in a shopping cart draped with a blanket.
The police are on the prowl, and the kids have no idea what their parents are capable of, so they decide to head for the Griffith Observatory on Mount Hollywood, hiding in the surrounding trees.
They make a makeshift campsite and debate their next course of action; Alex wants to get out of town, and Nico wants to save Karolina. The teens decide to mount a rescue while the PRIDE discuss the night's events.
They realize Karolina is Jonah's daughter and wonder where the Deans ran off to, contemplating Molly's powers and whether the danger they've put their kids into is worth their success. Tina comes clean about knowing of Gene and Alice Hernandez's murders, though she insists it wasn't her idea; Leslie acted alone.
PRIDE wants to find out what's really in the giant hole Jonah is digging, with the Yorkes deciding to investigate while the Wilders go to confront Karolina and Jonah at the church compound, determined to find out if she knows where the children are.
At the Church of Gibborim, Leslie and Frank have an open conversation about their mutual betrayals before they're interrupted by Jonah. Karolina sits in his bed, healing while wearing the same mask he did while he was crusty-skinned and needing of a sacrifice. He beckons the parents to leave so he can watch over his daughter.
While buying some thrift store clothes for the group, Chase and Nico talk about their new relationships. Chase admits that he's really into Gert and agrees to keep Nico's secret from Alex.
Speaking of Alex, he took a solo journey into the city that's not at all suspicious, but he does offer Gert a flier advertising older movies at a local theater including one relevant classic: Arsenic & Old Lace. Alex and Molly insist to Gert that her dinosaur can't join them when they finally hit the road to escape Los Angeles, prompting a heart-to-heart where she tearfully names the dinosaur before sending it off. Old Lace: it's official.
At Timely Coffee, the teens corner Leslie's assistant at the Church of Gibborim, trying to get help in finding Karolina. They try to convince him by informing him of the annual tradition of Gibborim teens going missing, hinting that it's a part of conspiracy. He refuses, and the kids decide to break into the church themselves.
Karolina comes to while Jonah sits at her bedside. She asks if her friends are safe, but Jonah diverts the conversation and reveals he is her real father. He promises to guide her with her new abilities, admitting that he himself doesn't feel alone anymore.
At the dig site, the Yorkes parents are using surveying equipment to learn more about what Jonah wants when they're interrupted by Leslie Dean. Their readings catch everyone off guard, as they determine whatever is down there is a living creature. Leslie didn't know, and she's disturbed Jonah kept a huge secret from her.
The Gibborim church recruiters are herding in their latest batch of runaway teens, with Chase and Molly sneaking into their van to infiltrate their ranks and find Karolina. The two are found by Vaughan, Leslie's church assistant, who's had a change of heart and decides to help the kids. He takes Molly and Chase to find Karolina, and they break her out of Jonah's secret room.
They get caught by the recruiters while attempting to escape, going on the run from church security guards. Alex, while attempting to steal a church van, spies on his parents who are attempting to interrogate Karolina. He overhears his parents admit they're working against Jonah now and want their kids to be safe. The Wilders confront Jonah, who tells them to have faith and that he will find their kids, but they don't buy it after the confrontation. Jonah intimidates them with his security guards surrounding them, leaving the Wilders no choice but to leave.
The teens break out as Alex pulls up with a van, getting back to their hideout with Karolina in tow. She and Nico discuss the mutual rescues and decide to continue their relationship. Alex goes missing, seemingly to call his parents, but instead he meets up with Darius. "The enemy of my enemy is my friend," he says, and the two make an alliance.
Vaughan meets up with Leslie Dean in secret, revealing that he told her about the Runaways cornering him at the coffee shop. She told Vaughan to help them get Karolina out of the church, undermining Jonah's authority. Meanwhile, Jonah receives a text from an unknown number: "Mission accomplished. Let me know what's next." But his surrounding is slightly hazy and out of focus — is this a flashback?
Dale and Stacey Yorkes discuss the living creature underneath Los Angeles, determining it's huge and old, maybe ancient. They decide to figure out how to reverse engineer Jonah's magic serum to find out a way to kill their leader when they are interrupted by the doorbell. It's time for an impromptu PRIDE meeting, sans the Wilders.
The Minorus, the Yorkes, and Janet Stein meet with Leslie, who apologizes for killing the Hernandezes and reveals what happened to Amy Minoru; Jonah killed her, and she knew the whole time. Leslie says that she sent the warning text to Amy, but it didn't help — no one actually knows what happened, except that Jonah killed her.
And though no one trusts Leslie now, she manages to unite them for one sole purpose. They are going to kill Jonah.
Speak of the devil, Jonah meets with Frank Dean in a mysterious, blank building that's housing the pod where Victor Stein slowly heals. They're both united in their efforts to keep Karolina safe, with Jonah promising a bright future. But he's getting a severe case of crusty skin once again, revealing that using his power so extensively could be the very thing that's killing him. They need Victor.
Alex returns to the campsite early in the morning, met by Nico while the rest of the teens sleep. He doesn't tell her that he met with Darius, but he does show what he got from his dad's rival — a wad of cash, enough to get out of town.
But Geoffrey Wilder has other plans, revealing to Catherine that he's going to make a call that will "change everything," promising to get his kids to safety so they can go to war with Jonah.
The kids head to the bus stop to hitch a ride out of town, followed by Old Lace who manages to stay out of sight inside a dumpster. Before they can determine where they're going, the TV airs a breaking news bulletin announcing an Amber Alert for Molly Hernandez. The Los Angeles Police Department has reported that Molly was last seen with the other five teens who are now being implicated in the death of Destiny Gonzalez from the beginning of the season.
As people start to notice the kids in the bus stop, they decide to stick to the series namesake and finally, they run away.
The series ends with the kids, followed by Old Lace, hauling ass through a Los Angeles alleyway while the last shot focuses in a crumpled newspaper. The headline reads: "Earthquake Watch: Is LA Next?"