The CW’s Arrow’s portion of the “Crisis on Earth-X” crossover event begins with the gathering of heroes deciding to interrogate their Nazi prisoner. He removes his mask and it’s revealed he’s Thea’s other brother (and Oliver’s best friend), Tommy Merlin. Earth-1’s Tommy died and Oliver (Stephen Amell), stunned to see this Tommy, asks to speak to him alone.
Elsewhere in S.T.A.R. Labs, the group tries to figure out whether these Nazis are anachronisms caused by the Legends screwing with time. Harry (Tom Cavanagh) reveals they’re probably from Earth 53, also known as Earth-X. On that Earth, the Nazis won the war and have taken over the world. These Nazis have now come to this Earth to wipe out the heroes.
Tommy and Oliver discuss the alternate versions of themselves, and Tommy explains they’re all born into the Reich and don’t have any choice about what to do with their lives on Earth-X. Tommy is a true believer and assures Oliver everyone he cares about will die horribly. He then kills himself before giving up any answers.
Dark Flash (Cavanagh) is at odds with Dark Supergirl aka Overgirl (Melissa Benoist) and Dark Arrow (Amell), as they’re known on Earth-X. It also turns out Overgirl and Dark Arrow are a couple.
Meanwhile, Felicity (Emily Bett Rickards) explains to Oliver she doesn’t want to be married to anyone. Oliver continues to insist he loves her and wants to marry her. Although Felicity assures Oliver she loves him, she’s adamant she wants to leave their relationship just the way it is now.
Jax (Franz Drameh) and Dr. Martin Stein (Victor Garber) have a heart-to-heart, and Jax admits he thinks of Martin as his father. He’s torn up over Dr. Stein leaving #TeamLegends. Alex (Chyler Leigh) and Kara also have a heart-to-heart over Alex’s break-up with Maggie. Alex reassures her sister she did the right thing and that if she really wants to have children, she was right in moving on.
Felicity’s also in the mood to reveal her feelings, telling Iris (Candice Patton) that her engagement to Oliver led to her being shot and that was the end of them. She doesn’t want that to happen again. As they talk, they spot the Nazis breaking into Dayton Optical Systems.
Arrow and Supergirl finally come face to face with their evil Earth-X doppelgängers, while The Flash (Grant Gustin) is astonished to see Earth-1’s Eobard Thawne (Cavanagh). With time travel, anything is possible according to Eobard. Overgirl taunts Supergirl, calling her weak, and Dark Arrow says his allegiance is to the fatherland and his wife, indicating Overgirl.
Arrow fires a kryptonite arrow at Overgirl, but she catches it before it does much damage. Still, that causes Supergirl to wonder why Arrow would have a kryptonite arrow in the first place. Dark Arrow and Overgirl send Supergirl off to save civilians, and Arrow hitches a ride with The Flash to help with the rescue. This is all a diversion so that #TeamEarth-X can take the prism they stole from Dayton Optical Systems away.
Felicity, Harry, and Caitlin (Danielle Panabaker) explain what the prism is and that it can be used to create a stable fusion reaction. That means it can be converted to a neutron bomb. Barry explains to the group that Earth-X’s villains include an evil Kara and an evil Oliver, as well as Eobard Thawne. They need to figure out where the Nazis are hiding and determine they can use Overgirl’s blood off Oliver’s arrow to track her.
Eobard is worried Earth-X’s Oliver will choose his wife over the Reich. Overgirl assures Eobard she’ll make sure Oliver makes the right choice, if and when the time comes.
Barry confesses to Iris that he’s been looking for closure but every time he sees Eobard, he thinks about his mother dying. Oliver interrupts to remind him they’re fighting their way through this together. Barry still thinks Oliver and Felicity are meant to be married. Oliver’s not sure. Of course, that’s when Felicity arrives to say they’ve found the Nazis.
Our heroes suit up and prepare for battle. It’s wall-to-wall Nazis inside the building, but they agree Overgirl has to be taken out of action first.
Felicity, Iris, Harry, and Caitlin man the command center. Mick (Dominic Purcell) is also hanging out there since he didn’t realize the team left to do battle. (He was busy eating.)
The battle’s underway inside the factory with lots of fighting going on between our heroes and the Nazis. However, Dark Arrow is missing from the action. It turns out he’s made his way to S.T.A.R. Labs while the heroes are being kept busy with Nazi soldiers. Overgirl leads the attack.
Mick takes on Dark Arrow and then Killer Frost tries to freeze his arm. #TeamArrow arrives to help, but Dark Arrow proves to be incredibly strong.
Over at the factory, the Nazis are down but Dark Flash and Overgirl are still in the fight. They’ve also got Metallo on their side, leaving our heroes outgunned. They’re taken prisoner, chained to a platform, with restraining collars around their necks. Eobard taunts Barry but Overgirl and Dark Arrow make him stop.
Overgirl’s having a difficult time standing and there’s something causing her an incredible amount of pain. Dark Arrow quietly reminds her they found what they need and it will be over soon. (There’s some real sizzling heat between Dark Arrow and Overgirl.)
It turns out what they need is Kara in order to save Overgirl’s life because she’s been exposed to too much solar radiation. Kara’s heart will save Overgirl. They stole the prism so they could weaken Kara to cut into her. Oliver threatens to kill Dark Arrow, but Dark Arrow knows the heroes won’t hurt them. Metallo zaps the chained-up gang.
The gang wake up to find they’ve been taken to Earth-X and placed in a large cage.