In a Nazi-ruled universe, Earth-X, a resistance group comes under attack by Dark Arrow. He wipes out all resistance members, and also kills the Earth-X version of the Guardian, but not before he says someone will end the Nazi regime. Dark Arrow finds a device on the resistance hideout.On Earth-1, heroes of Team Flash, Team Arrow and Legends contemplate about going to Barry and Iris’ wedding, and they all agree to go. On Earth-38, Kara is fighting a Dominator and defeats it. Afterwards, she and Alex are brooding over their lives in Kara’s apartment, until Alex sees the invitation to Barry’s wedding.
Initially both sisters aren’tkeen on going, but Kara decides they will, and takes her interdimensional extrapolator and opens a portal to Earth-1.In a manicure shop at Central City, Iris, Caitlin, Felicity and Kara are having their nails done and discuss about Iris’ wedding and others also suggest that Felicity would marry Oliver next (and the manicurist breaks her nail-maker on Kara’s fingers). In a dress-shop, Barry and Oliver are proving their suits, and Oliver is happy Barry is taking the step, and he also wishes the same for him. In S.T.A.R. Labs, Wells and Cisco have managed to create a formula that can separate the Firestorm Matrix from Stein and Jax. While Stein is thrilled, Jax is not enthusiastic, as it would mean he won’t have any powers.On Earth-X, everyone greets the Dark Arrow as Führer and he asks if the Nazis can get the device working. A female Nazi, Overgirl, appears, flying like Supergirl, and tells that they have one day.Just before Barry and Iris’ rehearsal dinner, Jax leaves S.T.A.R. Labs and Caitlin walks in to talk with Stein, who is working with something. Caitlin takes also some credit for the cure, that was made to break up Firestorm.
At the rehearsal dinner at CC Jitters, everyone greets each other, and Alex makes a closer acquaintance with Sara Lance, and they start drinking Scotch heavily. They are witnessed by Barry and Kara, with Kara claiming no one can drink Alex under the table (not knowing that no one has outdrank Sara either). Barry asks what’s going on with Kara, and she reveals what happened with Mon-El, and Barry can’t give her any advice on that. Barry then asks Kara to sing at the reception, and she agrees. Stein comes, and he privately reveals to Jax he was working on a compound, that will give him new superpowers after the Firestorm has been broken, but Jax is not thrilled about the possible abilities (it will allow him to stick to things). Joe holds a speech for the couple and points out that because of them, he openly reveals his relationship with Cecile. They toast, and outside, Sara and Alex are making out. Afterwards, Oliver proposes to Felicity, but she says no, claiming that while she loves him, she doesn’t want to marry him, yelling it for everyone to hear when he continues to push for it. Embarrassed, she leaves.
The next morning, Barry leaves quietly, making Iris breakfast in bed for her to wake up to, and it is shown how everyone has slept (with Felicity wishing she could airsleep like Kara). Sara and Alex slept the night together, but when Alex realizes it, she is embarrassed and attempts to leave quietly. Everyone gather at the church, and Kara worryingly waits for Alex to show up, as she shouldn’t be strolling on a different Earth. She eventually does, and claims she was okay, but can’t bring herself to admit what happened last night. Sara arrives and, despite Alex trying to not bring it up, Kara eventually figures out that they slept together. Alex is embarrassed, describing what she did as “such a guy thing to do” but Kara assures her she did nothing wrong and describes Sara as awesome, though is less approving of her being an assassin