Elseworlds: What to Know Before the Arrowverse Crossover

"Elseworlds" is nearly upon us. Kicking off tonight, the fifth annual Arrowverse crossover unfolds across three participating CW series: Supergirl, Arrow and The Flash.

In the three-night event, Barry Allen (Grant Gustin) and Oliver Queen (Stephen Amell) awake to discover they've switched bodies, and enlist Team Flash and Supergirl (Melissa Benoist) to find out what could have disrupted the timeline. Their search brings them to Gotham City, where Arkham Asylum doctor John Deegan (Jeremy Davies) is rewriting reality with the help of the mysterious Monitor (LaMonica Garrett). "Elseworlds" brings back Tyler Hoechlin as Superman, and introduces Ruby Rose as Batwoman, Elizabeth Tulloch as Lois Lane, and John Wesley Shipp as The Flash of Earth-90 (that is, The Flash from the 1990s TV show).

That would be enough to unpack on its own, but the crossover also takes place midway through the seasons of The Flash, Arrow and Supergirl. Just in case you haven't been following all three series, we'll bring you up to speed.

Supergirl

So far this year, the Girl of Steel faces a nemesis she can't just punch away: anti-alien sentiment. Under the guidance of Ben Lockwood's Agent Liberty, an international hate movement that calls itself the Children of Liberty is rising on Supergirl's world. While such feelings have long existed on Supergirl, the movement is at an all-time high this season, after President Olivia Marsdin was outed as a Durlan during an attack coordinated by terrorists Mercy and Otis Graves.

As a result, Marsdin was forced to step aside. Vice President Baker was subsequently installed as the new president of the United States. Though he was pleasant enough to Supergirl at first, this facade soon began to unravel. After the Graves siblings attacked a local fair using brainwashed aliens, which pulled the D.E.O. into a very public spectacle, he installed Colonel Lauren Haley to oversee operations. This seriously kneecapped D.E.O. Director Alex Danvers, who is no longer able to pursue threats without Haley's approval. Worse, both Haley and Alex are subject to Baker's whims, and he seems more concerned with his ratings and his donors than he does with national security.

This came to a head in the midseason finale "Bunker Hill." When Supergirl publicly arrested Agent Liberty, Baker's donors were upset, so he personally paid the D.E.O. a visit to berate Alex and Haley. Picking up on something Lockwood said -- specifically, that he was demonized for wearing a mask while no one knew who Supergirl really was -- Baker demanded full transparency from the Girl of Steel. She refused, due to the fact that those she loved could be hurt if her true identity fell into the wrong hands, and was forced to end her association with the D.E.O. despite Alex's protests.

As it stands, then, Supergirl has been cut off from the support system she's had since Season 1. It seems Alex, her sister and confidant, will remain at the D.E.O. with Brainiac-5 to mitigate the damage. Meanwhile, J'onn Jonzz, aka Martian Manhunter, continues to struggle with his desire to help people and his promise to his father that he would pursue non-violent ways.

Next Page: Arrow's Prison Blues

Arrow

As for Arrow, Oliver Queen is having a rough go this year. At the end of Season 6, Oliver voluntarily went to prison as part of a deal for the FBI's help in stopping Ricardo "The Dragon" Diaz as well as his friends' immunity. He spent the first seven episodes of Season 7 at Slabside Supermax Prison, where he found himself fighting his fellow inmates and guards alike. Ultimately, he was released from prison in exchange for his testimony against Diaz, but not before he had to fight for his life during a massive prison break that left Brick and Derek Sampson dead and many others injured.

While he was in prison, Team Arrow had a few issues of their own to deal with. For one, there's a new Green Arrow, who was revealed as Oliver's half-sister Emiko Queen in the mid-season finale. Thanks to Star City's anti-vigilante laws, SCPD Captain Dinah "Black Canary" Drake has had her hands full trying to capture and arrest Emiko, even as Rene "Wild Dog" Ramirez aids and abets her.

Meanwhile, Felicity has started down a dark path, where she has resorted to violence and fatal means to protect herself and her incarcerated husband. Her vicious new ways have startled even Oliver, who was shocked by how much she has changed during his months in prison. She has risked Anatoly Knyazev's life to achieve her own means; he subsequently gave her a gun, with which she intended to kill Diaz -- and only stopped because Laurel Lance convinced her not to because they needed him to secure Oliver's release.

John "Dig" Diggle, on the other hand, has enlisted at A.R.G.U.S. with his wife Lyla Michaels. Together with Curtis Holt, aka Mr. Terrific, they have discovered a powerful new threat: Dante and the Inferno, which suggests the Ninth Circle will rise in the back half of the season. Per the stinger at the end of the mid-season finale, Dig and Lyla will work with Diaz in order to glean information on Dante, as this mysterious new villain has been footing the bill for the Longbow Hunters' attacks.

Next Page: Meanwhile, on The Flash...

The Flash

Finally, on The Flash, Barry Allen and his team have been dealing with a metahuman serial killer they call Cicada. Cicada was created in the Season 4 finale, during the Thinker's Enlightenment. When Team Flash crashed Thinker's plan by destroying his satellites, they caused chaos throughout Central City. The debris landed at a local fair, injuring Cicada's niece and wounding Cicada himself; because the satellite was saturated with dark matter, the resulting injury gave Cicada a wound that can't heal, a dagger that can dampen other metahumans' powers and a few metahuman abilities of his own, including flight. Now, Cicada has made it his mission to kill every metahuman, as he believes they are the source of Central City's problems.

Cicada isn't the only disruption in Team Flash's lives. Nora West-Allen, Barry and Iris' full-grown daughter from the year 2049, has traveled back in time in order to get to know her father better. According to Nora, Barry disappeared in a "Crisis" in 2024 and has been gone ever since, meaning Iris raised her as a single mother. Now, Nora in Barry's present day learning how to use her speed powers under his tutelage, even as he struggles to come to terms with his future.

Even though Nora is a series regular this season, don't expect to see her in the crossover. "I am not in the crossover episodes," Nora actor Jessica Parker Kennedy told CBR. "I know! But I got to be such a huge part of the 100th episode, I feel like I can't complain at all." This is probably due to the fact that Barry and Oliver have switched lives, meaning that Oliver would have been the father and not Barry.

As to the rest of Team Flash, Caitlin Snow has seen the biggest transformation. Though the Thinker appeared to erase Killer Frost by suppressing Caitlin's meta gene, that wasn't the case at all. As it turns out, Killer Frost was born when Caitlin's father used experimental cryogenic gene therapy on her in order to prevent her from developing ALS; the Thinker simply used telepathy to bury Killer Frost's personality deep down in Caitlin's brain. After Caitlin's father resurfaced, Caitlin not only learned the truth about Killer Frost's origin, but also that her alter-ego still exists within her. As such, Team Flash has developed a way for Caitlin to call upon Killer Frost as needed. Better yet, Killer Frost isn't affected by Cicada's dagger, making her a key weapon in their fight against him.

Season 5 also has a new Harrison Wells in the mix. This year, it's Sherloque Wells, who calls himself the mutliverse's greatest detective. So far this season, he has worked with Ralph Dibney and Cisco "Vibe" Ramon to determine Cicada's identity. He also appears to be extremely suspicious of Nora, who -- as revealed in the series' 100th episode -- has been working with Reverse-Flash in the year 2049.

This year's Arrowverse crossover will involve the casts of Supergirl, Arrow and The Flash. The event will unfold over three nights, starting with a special episode of The Flash on Sunday, Dec. 9, at 8 p.m. ET/PT. It continues Monday, Dec. 10, with Arrow, and concludes on Tuesday, Dec. 11, with Supergirl.