The Flash-Supergirl crossover special: Here's everything we know about Kara and Barry's musical journey

The Flash Season 3 episode 17 is going to be a treat for Glee fans as it will see the reunion of three former co-stars of the musical. Darren Criss, Grant Gustin and Melissa Benoist will be featured on Tuesday's The Flash-Supergirl musical crossover, where Criss' Music Meister will put Barry in a coma along with Kara and the only way to return to reality is play along in the musical.

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Criss' Music Meister is not the typical villain that's usually featured on The Flash, and the actor described him as more troublesome than villainous.

"Come on, he makes people sing and dance. How mean could he be?" the actor said. "He's just kind of a troublemaker. I'll leave it at that. They've let me kind of do a lot of silly things on set, so considering how much they've allowed me to run with this, I have a feeling he won't seem as villainous."

The episode is titled Duet and it will see Mon-El and Hank Henshaw arriving on Barry's Earth carrying a comatose Supergirl. But before Barry can help them wake her up, the Music Meister surprises him and puts him in a similar coma. "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," the synopsis reads.

A promo for the episode shows Barry and Kara singing Super Friends, a song written by Rachel Bloom, the creator and star of The CW's Crazy Ex-Girlfriend. It talks about friendship and why Barry shouldn't go back in time to alter events.

The Flash airs Tuesdays at 8 pm ET on the CW.