The Flash And Supergirl's "Superfriends" Duet in New Musical Crossover Video

03/16/2017 04:18 pm EDT

ET went to the set of The Flash/Supergirl musical crossover, which airs next Tuesday and is titled "Duet."

In the video above, Melissa Benoist and Barry Allen preview the dreamy episode. "Well, we've gone back in time, as you can see," Benoist told ET, gesturing to her 1920s-inspired outfit. "And we're in this beautiful theater, Barry and Kara are stuck in a dream world and having to figure out shenanigans. They're on a journey. They're both on personal journeys sort of figuring things out together as a team."

"The crossover is just going to be a really good time," Gustin added. "There's going to be a lot of people brought together that you wouldn't otherwise see together. And we're not faking it -- this is actually our real background. All of us are trained in musical theater, so it's a real musical episode."

We also get to listen to the likeable duo singing "Superfriends," a song that was written by the star and creator of The CW's musical-infused comedy series Crazy Ex-Girlfriend, Rachel Bloom. And the tap dance routine they perform with the song was put together by Glee choreographer, Zach Woodley.

DARREN CRISS ("GLEE") GUEST STARS AS THE MUSIC MEISTER IN THE FLASH AND SUPERGIRL MUSICAL CROSSOVER – Barry (Grant Gustin) and team are surprised when Mon-El (guest star Chris Wood) and Hank Henshaw (guest star David Harewood) arrive on their Earth carrying a comatose Supergirl (guest star Melissa Benoist) who was whammied by the Music Meister (guest star Darren Criss). Unable to wake her up, they turn to Team Flash to save her.

However, the Music Meister surprises The Flash and puts him in a similar coma, one that Team Flash can't cure. Kara and Barry wake up without their powers in an alternate reality where life is like a musical and the only way to escape is by following the script, complete with singing and dancing, to the end.

Dermott Downs directed the episode with story by Greg Berlanti & Andrew Kreisberg and teleplay by Aaron Helbing & Todd Helbing.

MORE: The Flash, Supergirl Musical Crossover Details Reveal Characters' New Roles / The Flash, Supergirl Stars Gush Over Glee Reunion / Iris West Will Have Key Role In Musical Crossover

Based on the characters from DC, The Flash is from by Bonanza Productions Inc. in association with Berlanti Productions and Warner Bros. Television, with executive producers Greg Berlanti (Arrow, Supergirl), Andrew Kreisberg (Arrow, The Flash), Sarah Schechter (Arrow, DC's Legends of Tomorrow) and Aaron and Todd Helbing.

"Duet" episode of The Flash will air Tuesday, March 21 at 8 p.m. ET/PT.

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