The first episode begins with the creation of the Multiverse in the same way as the original COIE issues. Scenes from previous CW shows highlight both heroes and villains, including the previous crossovers.
Switch to Earth-89 and Gotham City and the Danny Elfman theme of the 1989 Batman film. Here we see the reporter Alexander Knox reading a paper with the headline Batman Captures Joker; he turns and views red skies, with the Bat Symbol in the sky.
Next to Earth-9 and San Francisco and we see Hawk and Robin from the Titans series.
Next to Earth-X from the previous CW crossover and the Ray heading towards an anti-matter wave.
Next to Earth-66 and Gotham City again where we find an older Dick Grayson (Burt Ward from the 60s Batman TV series) walking, presumably, Ace the Bathound, with the refrain from the show’s theme in the background. His world, too, suffers the red skies resulting in his cry of “Holy crimson skies of death!”
Earth-38 and National City, home to the CW Supergirl show and its heroes. Here we get a cameo from sci-fi actor Wil Wheaton shouting about the end of the world. Supergirl arrives to save him from a rampaging dragon which she manages to placate. She returns to the DEO where the team are trying to manage a worldwide earthquake before Martian Manhunter arrives and tells them the Monitor – whom they thought belonged to Flash’s universe – has arrived. They calculate they have until the following day to try and halt the anti-matter wave roaring through their universe and which is currently heading for Argo City, where Supergirl’s mother lives and where Superman and Lois Lane have gone to bring up their new-born son, Jonathan.
On Argo City, Superman and the others receive a warning from Supergirl as the red skies arrive and Alura – Supergirl’s mother – takes them to an escape pod which only has room for Kal and Lois’s son. As the pod launches, the wave hits and Argo is destroyed.
We head to Earth-1 and the island of Lian Yu where Green Arrow is instructing his daughter Mia when the red skies appear. They are blinded by a light as Harbinger appears to tell them that the Crisis has begun. In Central City, Flash attempts to contact his team when Harbinger appears to him to recruit him. In Gotham, Batwoman stops a robbery by the Wonderland Gang before she, too, is recruited by Harbinger. In Star City, White Canary and the Atom are enjoying trivia night at a bar when Harbinger appears.
Harbinger next appears on Earth-38 at the DEO with all the heroes and Superman and Lois who were saved by Harbinger at the last minute. After the heroes are introduced to each other, Harbinger tells them of the anti-matter wave and that Earth-38 is the tipping point where the Monitor wishes the heroes to make their stand. A massive tower appears outside National City and is designed to save the world. This tower needs to be protected against the coming army of the Anti-Monitor.
Meanwhile, Brainiac has calculated that Jonathan’s escape pod has ended up on Earth-16 in the year 2046. Despite Superman’s desire to get their son, Green Arrow convinces him he’s needed on Earth-38 to protect the tower; instead, Lois, Brainiac and White Canary head off to find Jonathan. At the same time, Martian Manhunter and Director Danvers are attempting to coordinate the evacuation of the planet’s population in the event of the tower falling, trying to get them to Earth-1.
Green Arrow bequeaths a new suit to Mia and wants her to continue after he is gone before meeting up with the Flash. When Flash tells Arrow that Flash is meant to die during the Crisis, Arrow angrily demands a meeting with the Monitor where he reminds him of the agreement they made where Arrow would die in place of Supergirl and Flash. The Monitor tells Arrow of the danger to the multiverse and how Arrow must prepare for every eventuality.
Back in National City, Alex persuades Lena Luthor to help them with the planned evacuation of Earth-38’s population while the heroes, led by Green Arrow, head to the Monitor’s tower and fortify it against the coming enemy.
On Earth-16, in 2046, White Canary, Brainy and Lois track down this world’s Green Arrow who has found and rescued Lois and Clark’s son.
At the Monitor’s tower, the heroes are attacked by shadow demons while Martian Manhunter and Dreamer coordinate the evacuation as Lena and Alex work on a transmatter portal. Superman and Supergirl aid the battle against the shadow demons, charging the tower with their heat vision, while the portal is completed. As the evacuation continues, Arrow and the other heroes hold their own against the shadow demons until the Monitor arrives and transports the heroes away. Arrow refuses to leave until everyone has been saved but is overrun by the demons.
On Earth-1, the heroes arrive in Star Labs and find Green Arrow dying, the Monitor having pulled him from Earth-38 moments before its destruction. They are joined by Nash Wells, now Pariah, and White Canary and the others. With his dying breath, Green Arrow, passes the torch to Flash and Supergirl, and the Monitor admits he did not foresee this ending.
 – Earth-89 is named for the Batman film released in 1989.
 – The “Batman catches Joker” headline is interesting as Knox is clearly older than when he appeared in the Batman film, at the end of which the Joker was killed. So either the Joker survived or there’s another one.
 – No immediate reasoning for the numbering of this Earth, but feel free to tell me I’m wrong.
 – Earth-X has a long history in DC Comics, appearing first in 1973 as a world where the Nazis won the Second World War or, in same stories, where the war was continuing.
 – Earth-66 is numbered for the camp 60s television show where Burt Ward appeared as Robin alongside Adam West’s Batman. Ward’s Robin would frequently use exclamations beginning with “Holy” followed by something relevant to the situation.
 – Ace the Bat-Hound first appeared in BATMAN #92 from 1955.
 – Earth-38 is home to Supergirl and her supporting cast and is probably named for the year of the first appearance of Superman, which seems a little unfair as it’s Supergirl’s show.
 – Earth-1 is the home of the Arrowverse shows that started with Arrow, then The Flash, then Legends of Tomorrow, and most recently at the time of writing, Batwoman. Supergirl originally ran on CBS and so wasn’t part of the Arrowverse until it’s second season when it moved to the CW.
 – Earth-16 was first shown on Legends of Tomorrow as a future timeline.