Supergirl & Flash Go Retro in New Musical Crossover Promo

In a new promo for "The Flash's" musical crossover with "Supergirl," Darren Criss' Music Meister traps Kara and Barry in a musical Matrix -- and the consequences could be deadly.

The promo also revealed three special "Arrow"-verse guests: Joe West, Malcolm Merlyn and Martin Stein. These actors will not be playing themselves, but rather musical mob boss villains of the Meister's making. It was also confirmed that Iris, who has a key role in the musical, will actually be a mobster's daughter.

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The musical will be set in the golden age of 1940s Hollywood and will feature a series of battles and traps that Kara and Barry must escape. What's worse, if someone dies in this musical world, they die in the real world. So much for Savitar being Barry's greatest threat this season!

According to the synopsis for the “Supergirl” episode “Star-Crossed,”

TERI HATCHER (“DESPERATE HOUSEWIVES,” “LOIS & CLARK: THE NEW ADVENTURES OF SUPERMAN”) AND KEVIN SORBO (“HERCULES”) GUEST STAR; DARREN CRISS (“GLEE”) MAKES HIS DEBUT AS THE MUSIC MEISTER – A new villain (guest star Teri Hatcher) comes to National City, putting Supergirl (Melissa Benoist) on high alert. Meanwhile, Winn’s (Jeremy Jordan) girlfriend, Lyra (guest star Tamzin Merchant), gets Winn in trouble with the law. Maggie (Floriana Lima) attempts to help Winn but old loyalties get in the way. The Music Meister (Darren Criss) attacks Supergirl. John Medlen directed the episode written by Katie Rose Rogers & Jess Kardos. Original airdate 3/20/2017.

According to the synopsis for “The Flash” episode “Duet,”

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. Original airdate 3/21/2017.

“The Flash” and “Supergirl” musical crossover will start with a lead-in scene on the March 20 episode of “Supergirl,” and continue in full on the March 21 episode of “The Flash.” The episode will include musical numbers from “The Flash” stars Grant Gustin, Jesse L. Martin and Carlos Valdes; “Supergirl” stars Melissa Benoist and Jeremy Jordan; and “Legends of Tomorrow” co-star Victor Garber and “Arrow” regular John Barrowman; along with “Glee” alum Darren Criss as the Music Meister, the episode’s antagonist.

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