The CW superhero crossover will begin with an episode of "Supergirl." Instagram/Melissa Benoist

Even before the official debut of “Supergirl” season 2 on The CW, the US network already confirmed that there would be a crossover with “The Flash,” “Arrow” and “DC's Legends Of Tomorrow." That string of episodes is now drawing nearer, as the superheroes gear up to fight evil together.

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The entire crossover, which will be a four-night, three-part series, will begin with an episode of “Supergirl” entitled “Medusa,” which will air on The CW on Nov. 28. The eighth episode in the season will see Alex coming out to her mother and Winn and James attempting to make a major decision regarding The Guardian.

It is not until the end of the episode, however, that Kara is visited by some surprise visitors. Guest stars Grant Gustin and Carlos Valdes, who play Barry Allen/Flash and Cisco Ramon/Vibe respectively, visit Supergirl’s town in order to enlist her help to fight off an alien invasion.

“Medusa” will get the wheels turning for the crossover, but Kara Zor-El will actually play a limited role in the events of the week. “You really are trying to run a single production across three different productions. But they’re run as three separate entities,” DC TV Producer Greg Berlanti said as much in an interview with IndieWire. “We have to figure out when we’re borrowing one actor from where. We’re telling one cohesive story.

“‘Supergirl’ will participate, but the storyline doesn’t actively begin there. There are some characters who show up in her episode, but the story begins with ‘The Flash’ episode and goes to ‘Arrow’ and ‘Legends of Tomorrow.’”

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“Supergirl” airs every Monday night, while “The Flash,” “Arrow” and “DC’s Legends Of Tomorrow” follow on Tuesday, Wednesday and Thursday nights respectively. All four series are air on The CW, but are viewable on Fox 8 for Australian audiences.