Exclusive: Check Out This First Look at A Photo From The Supergirl/The Flash Musical Crossover

Mon-El (Chris Wood) and J'Onn J'Onzz (David Harewood) bring an injured Supergirl (Melissa Benoist) to what looks like STAR Labs in this first look at a photo from The CW's forthcoming musical crossover between Supergirl and The Flash.

Cast members from Supergirl and DC's Legends of Tomorrow will head to The Flash on March 21 for an episode that will pit the titular heroes against the Music Meister, a villain originally created for Batman: The Brave and the Bold and played by Glee's Darren Criss.

The idea of a musical episode of The Flash has been floated since the show premiered, given the presences of Glee actor Grant Gustin and Rent performer Jesse L. Martin on the cast. Jordan and Benoist from Supergirl also come from musical backgrounds, so once Supergirl existed, questions about a musical episode for that show came up, too.

Little did fans know it would end up a crossover when it finally did happen -- and one to reach out and grab characters from other Arrowverse shows, too. ComicBook.com were the first to report that EP Greg Berlanti planned on using The Flash and DC's Legends of Tomorrow actor Victor Garber, who played a prominent role in the Berlanti-produced musical dramedy series Eli Stone, in the episode.

Actors who will sing in the musical include Grant Gustin (Barry Allen/The Flash), Jesse L. Martin (Detective Joe West), and Carlos Valdes (Cisco Ramon/Vibe), Melissa Benoist (Kara Danvers/Supergirl), Jeremy Jordan (Winn Schott), Arrow and Legends of Tomorrow's John Barrowman (Malcolm Merlyn) and Legends' Victor Garber (Martin Stein) -- as well as probably Criss.

Songs from the episode will be penned by fellow CW star Rachel Bloom (creator of Crazy Ex-Girlfriend), as well as the recent Oscar-winning duo of La La Land.

You can check out the official synopsis below:

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 (#317). Original airdate 3/21/2017.

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