The CW will unite the heroes of Arrow, The Flash, Supergirl and Legends of Tomorrow for an epic crossover event titled, Crisis on Earth-X and the promos and plot details are already out. Here is everything you need to know about The CW's four-episode event.

Crossover airdate

The event kicks off on Monday, 27 November with Supergirl season 3 Crisis on Earth X, Part 1 at 8 pm EST followed by Arrow season 6 episode Crisis on Earth X, Part 2 at 9 pm EST.

The event then continues to The Flash season 4, Crisis on Earth X, Part 3 airing on 28 November at 8pm EST, finally ending with DC'S Legends of Tomorrow, Crisis on Earth X, Part 4 at 9 pm EST.

Crossover Synopsis [Warning: Spoiler Alert]

The CW network has released the official synopsis for the 2017 crossover event, featuring all the Arowverse characters. Wentworth Miller will guest star as Citizen Cold, while Russell Tovey will make his debut as Russell Tovey in the chapter.

Read the full description here:

Barry (Grant Gustin) and Iris's (Candice Patton) wedding brings the gang together, but things go awry when villains from Earth-X attack the ceremony. All of the superheroes band together with help from their super friends like Citizen Cold (guest star Wentworth Miller), The Ray (guest star Russell Tovey), Felicity Smoak (guest star Emily Bett Rickards), Iris West and Alex Danvers (guest star Chyler Leigh) to take on their most formidable villains yet. Earth's mightiest heroes - Green Arrow (guest star Stephen Amell), Supergirl (guest star Melissa Benoist), The Flash (Grant Gustin) and White Canary (guest star Caity Lotz) - lead their teams into battle to save the world.

Plot details and leaked set photos

The Flash season 4
Barry Allen and Iris West wedding will take centre stage in the DCTV crossover event The CW

In the Arrowverse, Earth-X is a world where Germany won World War II and Green Arrow, The Flash and Supergirl are evil. It was first referenced in the Supergirl episode Worlds Finest. The crossover plot is set to revolve around the heroes facing their own evil versions from Earth-X, a world where the Nazis won World War II.

Leaked set photos have revealed that actor Tom Cavanagh will appear as the Earth X's Flash aka The Reverse Flash, and Arrow's villain Prometheus from Earth-X will appear in the crossover.

The event will set up a new animated web series, Freedom Fighters: The Ray which is set to premiere on CW Seed in 2017, and will be set within the shared Arrow multiverse.

Arrowverse executive producers on the event

Arrowverse crossover poster
The official poster for Arrowverse crossover titled, Crisis on Earth-X The CW/ DC TV

Executive producers Marc Guggenheim and Andrew Kreisberg opened up about the event to Deadline. "We conceived this year's crossover to be evocative of the annual Justice League/Justice Society crossovers we grew up with and looked forward to as kids. Phil was the perfect choice to bring the comic book cover iteration of this idea to life."

"You can count on one hand the number of artists who could compellingly represent so many characters in a single image. Phil is one of them. And his design invokes the cover ofJustice League #207, which was the 20th annual JLA/JSA crossover. Our 10-year-old selves are in heaven," the executive producer was quoted as saying by Deadline.