"Crisis on Earth-X" is the fourth Arrowverse crossover event, featuring episodes of Supergirl, Arrow, The Flash, and Legends of Tomorrow on The CW. The crossover began on November 27, 2017, with Supergirl and Arrow, and concluded on November 28, with The Flash and Legends of Tomorrow. In the crossover, Barry Allen and Iris West's friends visit Central City for their wedding, only for the ceremony to be interrupted by interlopers from the parallel universe of Earth-X, where the Axis powers claimed victory in World War II.
Development for a crossover of the four series began in December 2016 after the release of the previous crossover, "Invasion!". The premise and title of the crossover were revealed in September 2017 as production on the episodes began; elements from then upcoming animated web series Freedom Fighters: The Ray were part of the crossover, including the live-action appearance of Raymond Terrill / The Ray, the Freedom Fighters, and the New Reichsmen.
"Crisis on Earth-X" was met with critical acclaim with it being widely considered an improvement on the previous crossovers. The crossover was viewed by an average audience of million viewers per episode. A subsequent crossover aired the following year, titled "Elseworlds".
Plot
Part 1 A Nazi regime rules the parallel world of Earth-X, where an archer known as Dark Arrow is the Führer and leader of the cabal known as the New Reichsmen. He seizes a temporal gateway from the Freedom Fighters, which enables travel to other universes. On Earth-1, Barry Allen and Iris West's friends, including Kara Danvers and Alex Danvers from Earth-38, come to Central City for Barry and Iris's wedding. Harry Wells, Cisco Ramon, and Caitlin Snow develop a serum to separate the Firestorm matrix from Martin Stein and Jefferson Jackson. However, Jefferson is reluctant to give up being Firestorm, while Stein is thrilled at the prospect of being able to live a normal life with his family. Oliver Queen re-proposes to Felicity Smoak, but she is hesitant about marrying him. The wedding ceremony is interrupted by invaders from Earth-X led by Dark Arrow, his Kryptonian wife Overgirl, and the Earth-X analog of Prometheus. After Alex and Sara Lance capture Prometheus, the Nazis retreat. Dark Arrow and Overgirl, who are doppelgängers of Oliver and Kara respectively, discuss their next step with Eobard Thawne, Barry's speedster nemesis who was previously presumed dead.
Part 2 In S.T.A.R. Labs, Prometheus reveals himself as Tommy Merlyn's Earth-X doppelgänger, and taunts Oliver before taking a suicide pill out of loyalty to the Führer. Harry reveals that, through his exploration of the multiverse, he discovered that Earth-X is a dystopian world where the Allied forces lost World War II. Dark Arrow, Overgirl, and Thawne steal an experimental sub-light generator, the Prism, from a research company. Oliver's team, along with Harry, Killer Frost, Cisco, and Mick Rory, are held captive at S.T.A.R. Labs after the Nazi forces occupy it. Oliver, Barry, Sara, Martin, Jefferson, and Alex are taken to a concentration camp on Earth-X, while Kara is moved to S.T.A.R. Labs. Overgirl is dying from disproportionate solar irradiance in her heart, and Dark Arrow plans to use the Prism, powered by S.T.A.R. Labs' particle accelerator, to create artificial red sunlight that can weaken both Karas' invulnerability, allowing Thawne to transplant Kara's heart to Overgirl.
Part 3 In the concentration camp, the heroes are rescued from execution at the hands of SS-Sturmbannführer Quentin Lance by Ray Terrill and Leo Snart, Leonard Snart's doppelgänger. Thawne prepares to operate on both Overgirl and Kara, and Iris and Felicity work to rescue their friends at S.T.A.R. Labs. General Winn Schott, the commander of the Freedom Fighters, is determined to strand Dark Arrow and Overgirl on Earth-1 by destroying the temporal gateway. While posing as Dark Arrow, Oliver discovers that the Nazis possess a doomsday device in the form of a timeship called Wellenreiter, a militarized equivalent of the Legends' Waverider. Oliver allows the timeship to enter Earth-1 to avoid jeopardizing his cover, but he is ultimately exposed when he refuses to kill Felicity's Earth-X doppelgänger, a concentration camp prisoner. The heroes struggle against both the Freedom Fighters' Red Tornado, deployed by Schott as a failsafe, and the Nazi forces, and Martin opens the gateway at the cost of being mortally wounded.
Part 4 The heroes return to Earth-1, and Iris, Felicity, Kara, and the others are rescued by the returned heroes and the Waverider crew. Jefferson is also affected by Martin's injuries, so Martin uses the serum to separate the Firestorm matrix, dying from his wounds. Jefferson tells Martin's family of his fate; they, along with the Legends and Barry's team, are devastated by Martin's death. His death spurs the heroes to declare war on Earth-X's Nazi forces. When the Nazis attack Central City, the heroes counter their assault. Harry, at the helm of the Waverider, destroys the Wellenreiter after the heroes disable its shield. Barry spares Thawne and allows him to escape; Thawne vows to return. During the battle with Kara, Overgirl's solar radiation goes nuclear, and Kara carries her into space, where her body explodes, killing her; Oliver, despite giving Dark Arrow a chance to stand down, kills his grief-stricken doppelgänger soon after. After Martin's funeral, Kara and Alex return to Earth-38, Ray returns to Earth-X, and Leo decides to temporarily join the Legends. John Diggle, an ordained minister, officiates Barry and Oliver's weddings with Iris and Felicity, respectively.
Cast and characters
Main and recurring
+ Actor Character Episode Supergirl Arrow The Flash Legends of Tomorrow Melissa Benoist Kara Danvers / Supergirl rowspan="2" rowspan="2" colspan="3" Kara Zor-El / Overgirl (Earth-X) Mehcad Brooks Guardian (Earth-X) colspan="3" Chyler Leigh Alex Danvers colspan="3" Jeremy Jordan Winn Schott colspan="3" Winn Schott (Earth-X) colspan="2" Chris Wood Mon-El / Mike Matthews colspan="3" Stephen Amell Oliver Queen / Green Arrow rowspan="2" rowspan="2" rowspan="2" colspan="2" Oliver Queen / Dark Arrow (Earth-X) Victor Garber Martin Stein / Firestorm colspan="3" Emily Bett Rickards Felicity Smoak / Overwatch colspan="2" Felicity Smoak (Earth-X) colspan="2" Caity Lotz Sara Lance / White Canary colspan="3" Tom Cavanagh Harrison "Harry" Wells rowspan="2" colspan="2" rowspan="2" rowspan="2" Eobard Thawne / Reverse-Flash Dominic Purcell Mick Rory / Heat Wave colspan="2" Candice Patton Iris West colspan="2" Franz Drameh Jefferson "Jax" Jackson / Firestorm colspan="3" Danielle Panabaker Caitlin Snow / Killer Frost colspan="2" Carlos Valdes Cisco Ramon / Vibe Grant Gustin Barry Allen / Flash colspan="2" Echo Kellum Curtis Holt / Mister Terrific Rick Gonzalez Rene Ramirez / Wild Dog Juliana Harkavy Dinah Drake / Black Canary colspan="2" Frederick Schmidt Metallo (Earth-X) Wentworth Miller Leonard "Leo" Snart / Citizen Cold (Earth-X) colspan="2" colspan="2" Russell Tovey Ray Terrill / The Ray colspan="2" colspan="2" Brandon Routh Ray Palmer / Atom colspan="3" Maisie Richardson-Sellers Amaya Jiwe / Vixen colspan="3" Amy Louise Pemberton Gideon (voice) colspan="3" Tala Ashe Zari Tomaz colspan="3" Nick Zano Nate Heywood / Steel colspan="3" Only those who appeared in multiple episodes are listed on the table. Despite being credited, Katie McGrath and Odette Annable do not appear in the Supergirl episode, and David Ramsey and Katie Cassidy do not appear in the Arrow episode.
Guest Supergirl Jesse L. Martin as Joe West Keiynan Lonsdale as Wally West / Kid Flash Jessica Parker Kennedy as a caterer Danielle Nicolet as Cecile Horton Patrick Sabongui as David Singh William Katt as the minister
Arrow Colin Donnell as Tommy Merlyn / Prometheus (Earth-X)
The Flash Paul Blackthorne as SS Sturmbannführer Quentin Lance (Earth-X)
Legends of Tomorrow David Ramsey as John Diggle Susanna Thompson as the Wellenreiters A.I. (uncredited)
Production Development and filming
Planning for the yearly Arrowverse crossover began in December 2016, with Arrow showrunner Wendy Mericle saying, "We actually sort of do, believe it or not, have a concept for what we want to do for next year's crossover. It's crazy". By February 2017, planning began for a true four-way series crossover. Because each series was renewed for an additional season, the producers could plan production schedules to incorporate the crossover. Executive producer Andrew Kreisberg said, "One of the big things we learned from "Heroes Join Forces", which made "Invasion!" slightly easier, was building in shut-down days, where shows just went dark. The single hardest factor in doing the crossovers is actors' availability because the shows keep going on. You're basically juggling four shows' worth of schedules." That May, Mark Pedowitz, then president of The CW, confirmed that there were no plans to incorporate Black Lightning in the crossover, as it was not part of the Arrowverse at the time and was scheduled to debut in the middle of the 2017–18 television season.
In June 2017, executive producer Marc Guggenheim noted that it would be hard to top the threat of aliens in "Invasion!", so this crossover would aim to "increase the emotional stakes and the emotional payoffs". In September, it was revealed that the title of the crossover would be "Crisis on Earth-X" and that Russell Tovey as Ray Terrill / The Ray would make his live-action debut in the Arrowverse, ahead of appearing in the animated web series, Freedom Fighters: The Ray, along with other characters and concepts from that series. Guggenheim, who developed Freedom Fighters for CW Seed, felt that employing Earth-X in the crossover due to fitting into the plans of what the showrunners wished to make for a crossover that had the heroes being evil in another world, as they could have made another parallel universe but instead opted to use an idea that had already been implemented. The producers knew from the beginning of the crossover's conception that they wished to have the Arrowverse's heroes be villains in Earth-X. In 2019, Guggenheim called "Crisis on Earth-X" the "gold standard" of the yearly crossovers.
Filming of the four episodes began on September 22, 2017. Supergirls episode was directed by Larry Teng, Arrow by James Bamford, The Flashs by Dermott Downs, and Legend of Tomorrows by Gregory Smith.
Writing The crossover's story was conceived by Kreisberg and Guggenheim. The teleplay for Supergirls episode was written by showrunners Robert Rovner and Jessica Queller, Arrows by showrunner Wendy Mericle and Ben Sokolowski, The Flashs by showrunner Todd Helbing, and Legends of Tomorrows by showrunner Phil Klemmer and Keto Shimizu.
In August 2017, Mericle added that the crossover would be "very much rooted in the DCU". At the Television Critics Association press tour in August 2017, Pedowitz said that the crossover would involve romance, with Berlanti adding, "our way of making the show bigger this year was to go even more personal, so it's a big life event for a few different people on the show. There are many life events that happen." Mericle described the story as one where the character of Oliver Queen "explores the question of true love". "Crisis on Earth-X" did wrap up several story arcs including the weddings of Oliver Queen and Barry Allen, Alex Danvers getting over her ex-girlfriend, and Martin Stein leaving the Legends.
In September 2017, in a statement revealing the crossover's title, Guggenheim and Kreisberg said that the crossover was conceived "to be evocative of the annual Justice League/Justice Society [comic book series] crossovers we grew up with and looked forward to as kids".
Casting