The Flash and The Green Arrow are under attack, and take cover alongside a building. When their attackers are revealed, it’s Supergirl, Spartan, Speedy, and several of the Legends.
Ten hours earlier, Wally speeds around S.T.A.R. Labs while Caitlin and Cisco check his stats and Joe and Iris observe. Wally is much faster than Barry was this early on. Iris wants them to hide how well Wally is doing, so he doesn’t rush into danger. Cisco is uncomfortable with lying to Wally, but Caitlin complies.
H.R. calls on the intercom, he wants them in the cortex. As they get ready to leave, Caitlin suggests she, Cisco, and Barry go out for drinks. Cisco refuses, still blaming Barry for Dante’s death.
H.R. does a presentation, explaining he wants to offer tours of S.T.A.R. Labs, with extras such as reenactments of the particle accelerator explosion, from the particle’s perspective. As usual, no one is impressed. Suddenly, Cisco gets a satellite reading, a meteor is heading for Central City. Barry speeds away.
The Flash finds the meteor, which turns out to be an alien ship. Suddenly, Barry is blasted to the ground and numerous aliens emerge from the ship and stream into the city.
The news is reporting on the fallen ship the next day. Lyla is there on behalf of Argus, arguing with a woman about who will handle the ship. The woman leaves just as The Flash arrives. Lyla arranges to meet up with him at S.T.A.R. Labs.
The whole team is there when Lyla tells them about the aliens, who are known as The Dominators. They came to earth once before, in the 1950s. They abducted a number of people and left the planet. Now there are four ships on earth. One message was sent, claiming both a peaceful mission and threatening anyone who comes for them. Lyla wants Team Flash to stay out of it, though she offers to keep them informed. Once she leaves, Wally asks Barry what he plans on doing, knowing he will not stay out of it. Barry knows where to find help.
In Star City The Green Arrow and Spartan are fighting Vigilante, who shoots at them. The Flash speeds in and grabs them both, bringing them to Felicity’s apartment. He tells them about the aliens. Thea is also there, in need of Ollie for mayor duties. She is so excited about aliens that she decides to suit up as Speedy again. They decide to also reach out to the Legends.
At a S.T.A.R. Labs hanger, they wait for the Legends to show up, since Felicity got a message to them. Barry and Cisco create a breach to find Supergirl.
In Kara’s apartment, Barry and Cisco wait for her to return. She soon does, and Barry asks Kara for help.
Most of the Legends join the group, with Nate and Amaya staying behind on the Waverider. When they meet Supergirl, no one believes she is an alien. Until she flies into the air and burns her logo into the floor with her heat vision.
The Dominators set up a device in what looks like an abandoned building. They plan on taking the human leader.
Kara is somewhat familiar with the Dominators, apparently a long time ago they came to Krypton. They decide they need a leader, and Cisco votes for Ollie. Ollie however insists that Barry lead, since he gathered them. Barry is a bit unsure, and Ollie helps him get everyone started training against Supergirl.
Barry gives Supergirl and Ollie a proper introduction. Ollie insists she not hold back, especially with him.
Ray shows Cisco his new Atom suit. Cisco offers upgrades. When Barry walks over, Cisco excuses himself. Barry asks about Snart, and Ray tells him how Snart died.
Iris sees Wally outside the hanger. H.R. told him the truth about how well he is doing, but Iris insists that Wally is not ready. They argue and he speeds away.
Felicity notices the tension between Cisco and Barry. Cisco tells her what happened to Dante because of Flashpoint.
Martin and Jax ask to speak to Barry alone, though Barry insists that Ollie can listen too. The four of them go off by themselves, and Martin and Jax play the recording they found on the Waverider. Old Barry on the recording tells them that he changed things by traveling in time, and they should not trust anyone. Including Barry. Barry explains Flashpoint. Jax thinks he should come clean to everyone, but Ollie says they should wait until the Dominators are defeated.
As they head out to rejoin the others, Martin has vision of the same young woman he’s been seeing for a while. Caitlin finds him, and Martin asks her to accompany him to his house.
Supergirl kicks everyone’s ass in training.
Lyla has a meeting about the Dominators with a bunch of suits, including the woman from before and the President of the United States. The President agrees with Lyla’s plan of attack and leaves. An old man wearing glasses tells Lyla that Amanda Waller always listen to him, and Lyla would be smart to do so as well.
The Dominators attack The President’s car, abducting him.
Joe finds Wally at S.T.A.R. Labs, looking up his stats. Wally is upset that no one has been honest with him about how well he is doing besides H.R. He thinks Joe and Iris don’t have faith in him.
In the hall, Wally asks H.R. to train him. H.R. refuses, since he believes he would just be sent back to his own earth if that happened.
Caitlin tells Martin about Killer Frost as they walk up to his house. Martin promises to help her if she needs. They get to his door, and are greeted by the same woman Martin keeps seeing in his visions. The woman calls him “Dad.” Martin excuses himself quickly and leaves.
Cisco finds the recording of old Barry and listens to it.
Cisco finds Barry training with the others, and is furious at him for keeping secrets again. They argue until they’re overheard, at which point Barry explains Flashpoint to everyone. Diggle is stunned that John Jr. used to be a girl.
Lyla texts about the President. Knowing there are trust issues now, Barry offers to sit out the fight. Ollie stands up for Barry, saying if Barry stays behind he will too. Diggle tells Ollie that they can both stay behind, and everyone else leaves.
They find the building where The President is being held, and Supergirl confirms he is inside. Mick calls Supergirl “Skirt” and they banter a minute before entering. They find The President quickly, but he was only being used as bait and the Dominators vaporize him. They turn on their weapon, and all the heroes start to glow from the forehead.
Barry shows Ollie the newspaper article from the future. Iris West-Allen is no longer the author, something else Flashpoint changed. Ollie describes his parent’s deaths, telling Barry that he would have done the same thing. Cisco calls them because S.T.A.R. Labs is being attacked.
Outside, The Green Arrow and The Flash realize the attackers are their friends, who are being mind controlled by the Dominators. The Flash tries to fight everyone with powers while The Green Arrow takes on everyone else.
Cisco, Caitlin, Joe, Iris, Wally, and H.R. watch on the monitors. Wally decides he has to help and ignores everyone while he speeds out.
Wally does well in the fight at first, calling himself Kid Flash. But he is eventually knocked out.
Felicity and Cisco trace the signal controlling everyone. The Flash asks The Green Arrow to hold everyone off, and try to get Wally to the bunker. The Flash taunts Supergirl and races away, with her following just as fast.
The Green Arrow carries Wally inside, occasionally putting him down to fight. When he runs out of arrows, he fights with his fists.
The Flash leads Supergirl to the building the Dominators were in earlier. He taunts her, trying to make her angry. She sees The Flash in front of the device the Dominators set up earlier, and when she lunges at him, she passes right through. It was a speed mirage, and when trying to attack it, Supergirl destroys the device. The glow leaves her face and she returns to normal. As does everyone else chancing The Green Arrow and Wally.
Wally walks through S.T.A.R. Labs when he finds Joe and Iris. He expects them to be mad at him, but mostly they’re relieved he is okay. Privately, H.R. agrees to train Wally.
Supergirl scans Central City for more mind control devices while The Flash returns to the others, they meet outside. Suddenly White Canary is surrounded by light, then she vanishes. The same thing happens to The Atom, Spartan, and Speedy. Everyone left runs for cover, and the same light appears around The Green Arrow. The Flash tries to grab him, but is not fast enough, and Ollie is abducted too.
The ultimate four-show crossover continues tomorrow evening with Arrow on The CW at 8/9c.