"Elseworlds, Part Three" starts immediately after last night's events. The version of Superman — Deegan, who's posing as the Man of Steel — they encounter unveils that The Monitor gifted him the Book, allowing the Man of Steel to rewrite reality. The two sides almost fight until Oliver crafts a way to get away.
In this new reality, we see that Superman's taken over STAR Labs, where John Diggle and Caitlin Snow work. Superman arrives at the lair and is upset Barry and Oliver got away. superman goes into the pipeline, where Kara's being held captive. Kara tries breaking out of the facility until Alex Danvers arrives and uses a sonic-based device to momentarily render her incapacitated.
Barry and Oliver decide they have to try and track down Cisco so that he can help them vibe to Earth-38 and find the real Superman. They arrive at Cisco's apartment and when they go in, they're seemingly transported to another reality where The Monitor is waiting to greet them. The two are prompted with an offer to help the Monitor face the greater threat he previously spoke about but they refuse. He teleports them back into the reality that Deegan has created.
The duo decides that since in this reality that good guys have turned bad, they believe Cisco is probably "bad" in this reality as well. Using Barry's expertise, the two descend on a local watering hole where criminals typical hang out. There, they find Gary as a bartended and stumble across Cisco, who's apparently a drug kingpin in the reality. Cisco's primary henchman is James Olsen.
A quick fight breaks out between Barry and Oliver and Cisco's henchmen before the two reveal they know Cisco's brother. Knowing that something is up, Cisco pulls them into the back room. There, Barry tells him that they can teach Cisco how to use his powers to teleport them to other Earths.
Kara's still imprisoned while Alex and Caitlin have a conversation immediately outside her cell. Alex reveals that she's straight in this reality and Caitlin tells her that she'll take over her shift for the remainder of the night.
Cisco's able to use his powers to teleport the two to the Fortress of Solitude on Earth-38, where they inform him of the reality change on Earth-1.
Kara's still trying to get Alex's attention and reveals a childhood secret and Alex realizes that something's wrong with the entire situation. Alex releases Kara from her cell and on their way out, the pair runs into Deegan, Diggle, and Caitlin. He's about to use his laser vision to burn the sisters to a crisp when the heroes from Earth-38 vibe back in and stop him from doing so.
The two versions of Clark Kent fly off to fight each other and Alex tells Barry and Kara she'll lead them to Deegan's Book. Kara's unable to rewrite reality herself so she takes the Book to Clark. Together, Clark and Kara beat Deegan and Clark begins to rewrite reality using the book.
Everyone's powers revert and Barry speeds to where Kara and Clark are. Deegan flies back in and starts choking Barry out until Clark ends his reality rewrite. Deegan is able to fly away with the Book, leaving Barry uninjured.
Deegan begins rewriting reality and Barry mention that if he and Supergirl travel around the world opposite ways at Mach 7, they'll slow down time enough to get the book from Deegan. Superman tries to stop them by saying that he saw the pair die in the book, but they race off to continue anyway.
Oliver goes back to the apartment building where the met The Monitor. There, Oliver confronts The Monitor, asking him to help save Barry and Kara, namedropping the Crisis in the process. The Monitor asks Oliver how he would propose they keep the balance.
Superman finds Deegan and the latter is able to bring Amazo into this reality. Amazo blows Superman back and Lois vibes onto the scene with Brainiac-5 and Martian Manhunter.
Barry and Kara begin to race around the world while the fight between the Earth-38 heroes and Deegan continues. We see time begin to slow down as Kara and Barry's faces start lighting up as happened in Superman's vision of the future. Just as they're about to blow up, Oliver arrives on-scene and uses an arrow to shoot the Book out of Deegan's hands. Deegan's soon consumed by the energy of the book.
The group gathers at STAR Labs and sends the Earth-38 heroes back home. There, Clark and Lois tell Kara that they're having a baby. Because of the Kryptonian nature of the pregnn=ancy, Clark tells his cousin that he and Lois will be moving to Argo on a more permanent basis.
Later that night, Clark proposes to Lois in the Fortress of Solitude.5comments
Barry and Oliver go out for a drink back on Earth-1. The two share a heartfelt moment about the true meaning of heroism. As theey say a toast, Oliver's phone starts going off. He answers and it's Batwoman. Kane informs Oliver that Deegan's made a friend in Arkham. There, it's revealed that Deegan and Psycho-Pirate are cell neighbors.
The end title sequence reveals that Crisis on Infinite Earths will be next year's crossover.