Flash/Supergirl Musical Crossover Details Revealed in ‘Duet’ Synopsis

The CW first kicked off its DC Comics shared universe with Arrow in 2012, followed two years later by The Flash - after its titular hero, Barry Allen (Grant Gustin), first appeared in the network's flagship superhero series. Since then, Arrow and The Flash have featured a number of crossovers, one of which acted as the launchpad for Legends of Tomorrow, while the most recent officially welcomed Supergirl to The CW - though Kara Danvers (Melissa Benoist) resides on Earth-38 rather than Earth-1. Still, while The CW has already had its mega-crossover for the season, the heroes are teaming up for The Flash and Supergirl's musical crossover.

It was previously announced that the musical crossover will start off with a short scene at the end of Supergirl's March 20th episode, 'Star-Crossed', and take place mainly in The Flash's March 21st episode, 'Duet'. Plus, it was confirmed the villain would be Music Meister, played by Darren Criss, who appeared on Fox's musical dramedy Glee alongside both Gustin and Benoist. Now, the official synopsis for 'Duet' offers more details about what fans can expect from the musical crossover.

The CW released the full synopsis for The Flash's 'Duet' - as well as the synopsis for Supergirl's 'Star-Crossed' - which reveals the predicament Barry and Kara will find themselves in thanks to Music Meister's powers. Take a look:

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.

Winn, James, and Kara, plus Barry Allen (The Flash) in the Supergirl Crossover

Although it's unclear how many musical numbers will appear in the episode, it was previously reported 'Duet' will feature two original songs, one penned by Crazy Ex-Girlfriend creator/star Rachel Bloom titled "Superfriends" and one written by La La Land duo Benj Pasek and Justin Paul called "Runnin' Home to You." Kara and Barry will sing the former song, with Barry soloing in the latter. Additionally confirmed to have singing roles are fellow Arrowverse characters Joe West (Jesse L. Martin), Cisco Ramon aka Vibe (Carlos Valdes), Professor Martin Stein (Victor Garber), Winn Schott (Jeremy Jordan), and Malcolm Merlyn (John Barrowman).

Based on this synopsis, we can guess that Supergirl gets "whammied" by Music Meister in the Girl of Steel's own episode, which will work as the inciting incident for the musical crossover. But perhaps the most intriguing aspect of the 'Duet' synopsis is the revelation that Barry and Kara will be stuck in an alternate reality after being blasted by Music Meister's powers - which was not part of the villain's skillset when he appeared on Batman: The Brave and the Bold. However, it's unclear whether or not all of the singing and dancing will take place in this alternate world, though that would explain the inclusion of Merlyn and Winn.

That said, this synopsis helps to make sense of The Flash and Supergirl set photos in which neither titular hero appeared, but their fellow heroes - Wally West aka Kid Flash (Keiynan Lonsdale), Vibe, and J'onn J'onzz aka Martian Manhunter - could be seen facing off with Music Meister. Still, we won't get an idea of how The Flash and Supergirl will blend their superhero elements with musical numbers until an official trailer for the crossover debuts. However, with the musical episodes set to air in just a few short weeks, we shouldn't have to wait too long.