Prometheus-X is revealed to be none other than Tommy Merlyn from Earth-X as Oliver is shocked and needs a minute alone with his evil version of his best friend. Harry reveals to the team that there is a 53rd Earth in the Multiverse, which is where these villains are from.
Tommy explains his past on Earth-X as Oliver tries to get him to collaborate. But Tommy refuses and messes with his feelings. He takes a cyanide pill to prevent Oliver from getting any answers out of him.
Elsewhere, Dark Arrow, Overgirl, and Dark Flash have a disagreement that almost goes bad. Kara calms Oliver down as she kisses him, revealing that on Earth-X, they are married.
The heroes keep looking for their Earth-X versions before they can harm more people. Oliver and Felicity have a chat about their relationship.
Stein pulls Jax to the side as he needs them to be on the same side at a time like this. Alex keeps getting awkward with Sara after their one-night stand as she feels bad about having moved on from Maggie so fast.
Supergirl, Green Arrow, and The Flash get confronted by their evil versions who are ready to battle. They start fighting, but Overgirl tries to destroy a building to get the heroes distracted.
The team continues to try and learn how their Doomsday weapon works. They get a track on where the Earth-X villains are and suit up to go after them.
Iris and Felicity have a talk about what Felicity is going through with Oliver. The team encounter a Nazi squad and begins to battle.
Dark Arrow breaks into Star Labs while the team continues to battle Nazi soldiers. But Overgirl summons Metallo to take them on.
They manage to defeat the heroes and block their powers. Dark Arrow promises Overgirl that they are close to winning. They are going to use Supergirl to save this Kara's life.
Felicity and Iris get surrounded by Nazi soldiers at Star Labs while the other heroes have been taken to Earth-X, to a concentration camp.