“Crisis on Earth-X, Part 2” picks up as the group approaches Prometheus-X to try and get more information when he removes his hood, revealing his identity as the evil doppelganger of Tommy Merlyn.
Oliver says he needs a second with Prometheus-X and the rest of the group goes up to the main area. Up there, Wells explains there’s a 53rd earth called Earth-X, an Earth in which the Nazis won World War 2.
Earth-X Tommy explains to Oliver that he was born into the Reich and the Fuhrer would kill his parents if he deserted. He goes on to tell Oliver that the Earth-X Nazis will kill all of Earth-Prime’s heroes. He then bites down on a cyanide capsule, committing suicide.
Back at the Earth-X rallying point in Central City, Dark Arrow tells Overgirl and Dark Flash that Merlyn has died and orders Dark Flash to get to work on finding the prism they’re after. The three let their egos get the best of them and find themselves in a standoff against each other. They cool off and part ways.
Back at STAR Labs, Felicity has called Curtis and asks for him to research what he can on the Nazis. Oliver walks in and approaches Felicity about the situation they found themselves in the previous night at the rehearsal dinner.
Felicity reiterates her stance on not wanting to get married. She says they have something great going and want to keep pushing forward. Oliver tells her again that he wants to get married, but Felicity urges him to respect her decision.
Jax, Caitlin, and Wells are working on ways to stop the parallel-universe Nazis when Stein walks in and requests the room. He speaks with Jax about how the pair have been at odds and ends since they’ve been talking about separating Firestorm. Jax confesses that Stein’s the closest thing he’s ever had to a dad and that’s the primary reason he’s upset that Stein wants to leave Firestorm.
Alex goes down the elevator at STAR Labs and is approached by Sara, and the two share another awkward moment.
Kara starts talking to Alex, who says the situation she found herself in with Sara was a mistake — it’s not like her to have a one-night stand. Kara tries to convince her otherwise.
Felicity is approached by Iris and the two discuss Felicity’s stance on marriage and the latter reveals that the beginning of the end between her and Oliver began when she was shot. An alarm starts going off and Iris sees that the Earth-X villains have broken into Dayton Opticals.
Oliver, Kara, and Barry go to the business in hopes of stopping the Nazis, but are greeted by Overgirl, Dark Arrow, and Dark Flash in the parking lot. It’s there the Earth-Prime heroes find out that Overgirl and Dark Arrow are evil doppelgangers of Kara and Oliver while Dark Flash is the evil doppelganger of Wells.
Barry and Dark Flash begin speeding around fighting while Oliver pulls out a kryptonite arrow to shoot Overgirl with. Dark Arrow orders Thawne to take the prism and speed away while Overgirl uses laser vision to cut apart the beams to nearby skyscraper under construction.
Kara holds up the heavier top part while Barry and Oliver work at stabilizing the rest of the skyscraper, allowing the evil doppelgangers to escape.
Back at STAR Labs, Felicity and Wells tell the rest of the team that the prism stolen would allow them to create a neutron bomb. Barry walks in with the arrow Oliver used to shoot Overgirl with hopes that the team can use the blood to track Overgirl’s whereabouts.
Felicity and Caitlin work with Wells to begin using the blood to track Overgirl, and they say they should have a location soon.
Barry and Iris are talking about Thawne’s return when Oliver walks in and talks to them about their never-ending love. Felicity walks in to tell them they have a location on the Earth-X villains.
The heroes begin suiting up to converge on the location while Felicity and Iris stay behind to keep watch. Mick walks in complaining about the lack of mustard on his sandwich, he’s been left behind while the other heroes go to stop the bad guys.
The group starts fighting with the Nazi henchmen while Barry and Kara work on taking down their counterparts. Oliver and Sara both wonder aloud where Dark Arrow is and we see him walk back the STAR Labs sign.
At STAR Labs, Wells runs into Dark Arrow in the basement and runs off the warn the others.
The group of heroes are still at the warehouse fighting Nazi henchmen, trying to stop the Earth-X villains from carrying out their plan of leveling Central City.
Mick tells Iris and Felicity to hide and tells Caitlin to turn into Killer Frost — they’re going to try taking down Dark Arrow.
Back at the warehouse, Oliver tries to shoot another kryptonite arrow at Overgirl but this time, she catches it and snaps it in half.
Mick approaches Dark Arrow and starts firing his heat gun at him. He’s able to distract Dark Arrow enough for Caitlin to sneak up behind him and freeze his hand to his bow. Dark Arrow is able to break free but the rest of Team Arrow — Curtis, Dinah, and Rene — show up to help out.
The group at the warehouse is able to stop all of the henchmen, but they’re approached by a green-glowing robot who knocks most of the team out.
The team awakes to find out they’ve all been restrained with power-dampening necklaces by the group of Earth-X villains.
Overgirl walks in to address the team, but doubles over in pain. Her husband — Dark Arrow — convinces her to be strong and stand as she interacts with their Earth-Prime counterparts.
It’s here we find out the Earth-X villains end game, Overgirl needs a heart transplant and Kara is the only person capable of donating that organ. They’ve taken the prism to replicate a red sun that would weaken Kara enough to cut into her and take the heart.
Iris and Felicity are walking in the bottom hall of STAR Labs when they see Nazis putting the knocked out members of Team Arrow into the STAR Labs holding cells.
The heroes at the warehouse — Oliver, Barry, Sara, Stein, Jax, Kara, and Alex — wake up in a concentration camp on Earth X.