The episode opens with the same scene Flash ended within the prior episode. Flash from Earth 90 crawls across the ground, reaching for a book, but it’s already been stolen by a mysterious creature, who claims that everyone will soon perish.
We switch to a man named Dr. John Deegan teaching a class on psychology. He begins talking about ways to help patients through copying DNA like structures of those that are “super” or “meta.” However, his talk doesn’t go over very well, and the other professors storm out of the room. They call him Dr. Frankenstein.
Defeated, Deegan walks to his car and encounters the creature from earth 90, who needs Deegan’s help. He tells Deegan to use the book from Earth 90 to shape the world as he sees fit. Although hesitant at first, Deegan takes on the challenge. He opens the book, realizing the universe is literally in his hands.
We then open on Oliver waking up in a strange bed, with a strange voice calling from the other room. He looks around and realizes he his in Barry Allen’s house with Iris, and Iris thinks she is his wife! He asks where Barry is, before realizing that he IS Barry.
Iris gets an alert of a break in and leaves the house in a rush. Oliver begins looking around and then realizes he has Barry’s speed as well. Iris comes back and throws Oliver the ring for his suit, and Oliver tries it on.
Oliver starts to run and can hear Cisco in his ear telling him to go deal with the break-in. Oliver is unsure what to do, but ends up figuring out The Flash’s powers well enough he throws a lightning bolt. Except he misses. Cisco says the cops are on their way, and to let them do the rest, so Oliver flees the scene.
At Star Labs, Oliver gets checked out by Caitlin who says he’s perfectly healthy. Oliver tells the team that he’s going to see “Oliver Queen” in Star City.
The next scene opens with Barry Allen getting beat up by Diggle, who is calling him Oliver. Barry quickly realizes he has super strength and has somehow become the Green Arrow.
Barry tells Diggle he needs to make a call to Star Labs, but there’s an alert from the system. Diggle sees it’s an issue deep within the Glades and asks Barry to help, and Barry reluctantly agrees, even though he doesn’t know how to put the green suit on.
They head to the Glades and Barry struggles through using the Green Arrows abilities, just as Oliver had with The Flash’s. Diggle and Barry are about to lose the fight when Oliver appears and snatches them away with his speed.
Barry and Oliver have a conversation about what possibly could be happening.
They take the issue to Star Labs, where they try and get Team Flash to believe they’ve somehow switched lives, but they Team has a hard time believing them. Barry and Oliver decide they have to get Iris on board first.
Oliver tries to talk to Iris and make her believe the situation, and Iris ends up drugging Oliver until that he passes out. Ralph then comes in and punches Barry, knocking him unconscious.
Barry wakes up in a cell inside Star Labs with Oliver knocked out beside him, with their powers dampened. Barry wonders if maybe it’s just Earth 1 where reality has been shifted.
Cisco tells Caitlin he thinks the weird psychosis is a result of potential weather changes. Suddenly, he is vibing involuntarily and sees the creature from Earth 90.
Barry and Oliver back up the pipes with short circuits the cell, and then Oliver has to figure out how to phase them through the glass. They go looking for the extrapolater to change Earth’s, but Iris has it.
Barry delivers a speech to get Iris to believe them about the switch, and she finally begins to trust them. Iris gives them the device and they hop over to find Kara on Earth 38.
The scene opens on the Smallville farm, with Lois Lane and Clark Kent trying to fix a truck, while Kara visits. Lois talks about her desire to write an article about her time on Krypton.
Kara and Clark talk about the difficulty of keeping their secret identities and Kara having to leave the DEO. Clark feels guilty that he left Kara alone to visit Argo.
Barry and Oliver appear and it’s clear Kara knows their true identities. Barry and Oliver get to meet Lois and Clark. They explain the situation on their earth 1.
We flip back to Earth 1, where a mechanical creature is about to destroy Frost and Elongated Man, but he flies away before he hurts them.
On the ranch, Oliver and Barry argue over how much training the other may or may not need with their new powers. Oliver doesn’t think Barry is taking their power swap seriously.
Back in Star Labs, the team tracks down the machine that attacked them. His name is Amaz-0, and he replicates meta powers. They realize Elongated Man and Killer Frost have both had theirs taken.
Iris talks to the team about how she believes Oliver and Barry switched lives, and Cisco says he agrees with her and tells them about the involuntary vibe he had earlier. They decide that everything happening must be connected.
There is an alert that Amaz-o has entered the city.
We switch back to the farm, where Barry and Oliver try to work out their differences. Oliver explains that he was upset over how lighthearted Barry could be while still using the GA’s powers since Oliver depends on trauma and darkness to help him.
Barry realizes his GA powers do work better when he’s angry, and Oliver’s Flash powers work better when he’s having a good time. They decide to start acting more like one another and Kara agrees, saying they have to act the part.
Cisco breeches to Earth 38 and tells them that Team Flash believes their story. He also tells them that they need The Flash and GA back to save the city. Clark and Kara all tag along.
Amaz-o is destroying the city when Superman, Flash, Green Arrow, and Supergirl get to the scene. Oliver keeps him off balance so he can’t replicate their abilities and Superman finishes him off…or so they think. Amaz-o reappears and has in fact, taken all their abilities and replicated them.
Barry steps into the leadership position and comes up with a plan, as Oliver speeds to Amaz-o and leads him astray. Cisco creates a virus to ruin Amaz-o from the inside out. Oliver gets him back to the Team and they hold him long enough that Barry can shoot the virus right into Amaz-o’s weak spot. He explodes.
The team congratulates Barry and Oliver for doing such a great job with each other's powers, and they thank Superman, who then leaves to return to Lois.
Barry and Iris have a private conversation, where Iris admits she’s afraid that Barry will lose himself in the Green Arrow. Barry promises that no matter what happens, he will always come back to her.
Cisco tells the team that the creature he saw in his vibe has to be connected somehow, so he shows Barry and Oliver what he saw. Somehow, in the vibe, the creature can see Barry, Oliver, and Cisco, and he tells them that there is nothing anyone can do to stop what’s about to happen.
Oliver says that the creature is in Gotham city and that they have to go there.
We pan out on Batwoman, standing atop the highest building in Gotham.