Summoned by a distress signal from Felicity Smoak, The Legends arrive in Central City in 2017 in time to rescue their friends from a Nazi invasion from Earth-X - a parallel Earth where The Nazis won World War II! Meanwhile, on Earth-X, Sara, Jax and Stein struggle alongside Oliver Queen, Barry Allen and Alex Danvers to escape back to Earth One...
General alternate reality tropes involving The Axis Powers winning World War II, Justice League of America #107 (Vol. 1) (basic plot, idea of Earth-X), The Flash #165 (Vol. 1) (Barry Allen's wedding is disrupted by a super-villain attack), Flashpoint (concept of Citizen Cold - the heroic Captain Cold), Final Crisis (concept of Overgirl - the Nazi Supergirl) the movie The Terminator (appearance of Earth-X Metallo, Black Canary name-drops it), All-Star Superman (a Kryptonian dying because of absorbing too much solar energy) and the comics of Len Wein.
Given that some scientists theorize that the energy released by a star going supernova less than 25 light years from Earth could cause catastrophic changes to Earth's atmosphere, the consequences of a supernova forming on Earth would probably be far greater than just the destruction of The American Midwest.
Barry just letting Thawne go is just plain lame.
Victor Garber gives a fantastic final performance as Martin Stein.
The scene as most of Team Flash, Team Arrow and The Legends fight Metallo is everything The DCTVU can be at its best - comic book action, brought to life with amazing effects work and fight choreography.
The silent montage of the various heroes reacting to Stein's death is also everything The DCTVU can be at its best - sentimental and hopeful, indulging in all our best angels. It is also artfully shot, with haunting music
Miraculously, the fifth-segment fight-scene gives everyone on all four series a chance to shine. It is well-blocked, well-acted and well-shot.
Trivia Of Tomorrow
The DC Comics Multiverse has a tradition of alternate realities where the Nazis won World War II. The first was Earth-X (Two) - an alternate version of Earth-Quality, which housed the superheroes published by Quality Comics who were later bought by DC Comics. Justice League of America #107 (Vol. 1) (October 1973) introduced this Earth-X, when The Freedom Fighters - a team formed to fight the Nazis after they developed mind-control technology - summoned The Justice League from Earth One to help them.
Following Crisis on Infinite Earths, Earth-X was folded into the unified DC Universe. It was revived as Earth 10 in The New 52 reality.
On Earth 10, the rocket carrying the last son of Krypton to Earth landed in a Nazi-controlled Sudetenland. This child became Overman - Champion Of The Fourth Reich. He lead a team of Nazi metahumans, including Overgirl - a human girl who gained Overman's powers after being injected with Overman's genetic material. Overgirl was introduced during the Final Crisis storyline.
Rather than the usual Legends of Tomorrow logo, this episode opens with a special Crisis on Earth-X logo.
Ray says that his ATOM suit embiggens as well as shrinking. Embiggen is a perfectly cromulent word, first introduced on The Simpsons, which means "to make bigger."
Mister Terrific makes reference to The Chandrasekhar Limit. This is the maximum mass of a stable white dwarf star. Once that mass is exceeded, an star will begin to collapse in on itself and go supernova. The official Chandrasekhar Limit is 1.4 times the size of Earth's sun.
When Supergirl confronts Overgirl during the final battle, she says "General. Would you care to step outside?" This is a nod to Superman II, when Superman said the same line when confronting General Zod. (Thanks to Christopher Evans for pointing that one out!)
Harry says that Kara must fly Overgirl, "up, up and away". This was a catch-phrase frequently said by Superman just before he started flying in various comics and cartoons.
After demerging as Firestorm, Jax experiences the pain of Stein's injuries from before they merged while Stein was bleeding to death. Caitlin says this is because their vitals are still linked, somehow, and that connection is the only thing keeping Stein alive.
The Waverider is tracking The Nazi Time-Ship using the extreme radiation signature given off by Overgirl's extreme exposure to solar radiation. Mister Terrific noted the readings they have are fast approaching The Chandrasekhar Limit - this means that Overgirl will become a supernova that destroys the entire American Midwest.
Green Arrow: Thanks for your help.
Citizen Cold: We're not done helping, yet. Our enemies are still on your Earth, Ollie.
Green Arrow: (uncomfortably) Don't call me that.
(Green Arrow walks off as White Canary steps forward, quickening her pace.)
Citizen Cold: Give it time. I'll get through that crusty exterior.
White Canary: No. You really won't.
Citizen Cold: (smiling) I was talking to you.
(Thawne is about to start cutting into Supergirl's skin. Something is stopping his scalpel, however.)
Dark Arrow: What are you waiting for?! Do it.
Thawne: I'm trying! I'm trying but...
(Close-up as we see a tiny figure, growing larger, standing on Kara's chest, holding up the scalpel blade.)
The Atom: Mitts off, Mengele!
(The Atom jumps up and grows to full size, punching Thawne before zapping him with a taser blast. Dark Arrow charges forward, but Ray side-steps the attack and tasers him as well. He smiles as he moves and pulls on Kara's restraints, freeing her from the hospital bed.)
The Atom: Hi. How are you? (looks up to Felicity) Oh. I got your S.O.S. - how was the wedding?
The Atom: Okay, I know I'm late to the party, but why have Nazi dopplegangers taken over STAR Labs?
Felicity: They're from Earth-X. They hate everybody. They want to steal Kara's heart. And they have this giant robot.
The Atom: Huh. I've actually fought one of those before. Little known fact - the suit doesn't just shrink.
(As The Atom is speaking, a Nazi guard comes up behind him and cocks his gun.)
(Before the guard can shoot, The Atom spins around and reaches out, his arm growing longer as his enlarged hand pushes the Nazi to the wall and knocks him out.)
The Atom: It embiggens.
Felicity: (To Dark Arrow, as she stands between him and Supergirl.) My grandparents didn't survive The Holocaust so the world could be ruled by Nazis. So if you want Kara, you've gotta go through me. And even if you do, you're not gonna win. Because we will not back down. We will keep fighting. So get the hell off our Earth while you still can!
(Black Canary and Cisco take cover behind a crate as Metallo attacks.)
Black Canary: This guy's like The Terminator.
(Cisco starts laughing.)
Black Canary: (angrily) Why are you laughing?!
Cisco: I just love a good pop culture reference in a moment of crisis. Also... that!
(Cisco points to where The Flash has run into the room as Firestorm and The Ray fly in behind him.)
Alex: I should have known better than to think that a wedding on another Earth is going to solve all of our problems.
Kara: Yeah, but... you know, fighting evil versions of ourselves does kind of put those problems in perspective, doesn't it?
Alex: Way to see the silver lining.
(Stein asks Jax to give him Cisco's cure for their powers.)
Jax: You're asking me to kill you, Grey!
Stein: I'm asking you to let me die so that you can live.
(Sara walks down the Hallway. Ollie is waiting for her.)
Ollie: How are you holding up?
Sara: I'll cry at the funeral.
Ollie: (taking her arm) Sara...
Sara: (firmly) I'm fine.
Ollie: We need to gather everyone. Overgirl is going to go nuclear and the Earth-Xers are going to use their Waverider to threaten Central City and leverage us into surrendering Kara.
Sara: How do you know that?
Ollie: It's exactly what I would do.
(Heatwave burns one of the Nazis with a fire blast. Citizen Cold runs up.)
Citizen Cold: Excuse me! You can't just go around roasting people!
Heatwave: Why not?
Citizen Cold: You ever heard of Due Process? Rule of Law?
(Ollie accepts Felicity's proposal and suggestion that they marry right now.)
Ollie: Uh, John, what do you say?
John: Are you kidding me, Oliver? I'm the guy that for the past six years has been trying to keep you two together. It's only fitting that I marry you.
Based on his flirting with White Canary and his kissing The Ray in F408, Citizen Cold is bisexual.
Ray Palmer refers to the events of L113 and how he once fought a giant robot. He also demonstrates how he can use his suit to become bigger as well as smaller, as he did in that episode.
Felicity Smoak's grandparents were Holocaust survivors.
Mick refers to the events of L208 and how he thought for a time that he was being visited by Leonard Snart's ghost.
Citizen Cold says that the Earth-X version of Mick Rory died in a police station fire, after running back in several times to pull police officers out of the fire.
The Ray reveals his full name as Ray Terill.
Martin Stein sacrifices himself to save Jax's life by taking Cisco's "cure" for Firestorm, from S308.
Ray Palmer has a picture of himself and Martin Stein, taken with an 19th century camera of the two of them dressed in cowboy garb. This photo was likely taken during the events of either L206 or L111.
Barry lets The Reverse Flash go.
Green Arrow kills The Dark Arrow.
The Ray returns to Earth-X.
Citizen Cold decides to stay on Earth One for a while, but promises he'll return home to Earth-X someday. He and The Ray part ways affirming that they love each other.
At Martin Stein's funeral, as everyone takes turns shoveling dirt onto the grave, Sara thanks him for believing in her as Captain, Caitlin asks him to say hello to Ronnie for her and Barry thanks him for helping get him out of The Speed Force.
Alex and Sara agree there's no chance of a relationship between the two of them but Alex does thank Sara for helping her put things in perspective. They wish each other well and say they're sure the other person can find someone they can be with for more than just a night.
In keeping with the running gag from previous encounters with The Flash, John Diggle throws up whenever he is moved at super-speed.
John Diggle was ordained to conduct weddings to marry his brother and sister-in-law. He officially marries Barry and Iris, with Ollie and Felicity acting as Best Man and Maid of Honor.
Iris wanted to be a ballerina when she was nine.
Diggle also marries Felicity and Oliver.
Felicity refers to the events of A416 and the fake wedding she and Oliver had as bait for a trap for Cupid.
Earth X - Star City - 2017
Earth One - Central City - 2017
The Fridge Factor
Averted as Zari, Killer Frost, Felicity Smoak and Vixen are the ones who take down the Nazi Waverider.
The Bottom Line
Easily the weakest of the four chapters, but only because it is overburdened in how much it has to accomplish. Between The Death of Martin Stein, an epic battle between the Nazi army and all of the main cast of heroes and two weddings, there is a lot to get through. Amazingly, it's all the minor subplots and character moments (such as Caitlin's farewell to Stein or the Alex/Sara romance resolution) that are handled the best. Still, despite its flaws, this is still a damn fine episode and proof positive that good, epic superhero stories can be told on a small-screen budget.