Before they were chosen to play superheroes on their respective CW series, Grant Gustin and Melissa Benoist were better known for their musical roles on the FOX television series GLEE. The inclusion of other musical talents across the Greg Berlanti universe of shows -- including such recognized theatre actors as Jesse L. Martin, Victor Garber, Jeremy Jordan, and Carlos Valdes -- made a musical crossover more of a question of "when" rather than "if." This Tuesday at 8PM ET/PT on The CW, it finally happens, as the worlds of The Flash and the Supergirl mix once again with a musical episode titled "Duet."

One of genre television's most famous "musical episodes" is the classic Buffy the Vampire Slayer episode "Once More With Feeling" which aired in 2001. A precursor to Joss Whedon's other works including "Dr. Horrible's Sing-A-Long Blog," that Buffy episode took place at a time when the show's characters were facing some crossroads. It's a similar case here -- the engagement of The Flash's Barry Allen (Grant Gustin) and Iris West (Candice Patton) is off, and Kara (Melissa Benoist) isn't the biggest fan of Mon-El (Chris Wood) after learning that he's been lying to her for nine months. What better way than a musical to sing away their feelings?

While The Flash's musical episode isn't quite Buffy's -- that's a really high mark to hit -- it is quite enjoyable, with Benoist and Gustin both packing super-power behind their vocals. The two work very well together and have great musical timing in addition to comedic timing; they also both have at least one solo each in the special. When the Music Meister (Darren Criss, taking over the role played by Dr. Horrible vet Neil Patrick Harris in one of the most memorable installments of Batman: The Brave and the Bold) puts them in this musical space and environment, it's up to Barry and Kara to figure out how to get out, without their super strength, super speed, or any powers other than brainpower and song. It's fantastic to see Darren Criss as a part of the "Arrowverse;" whether one loved Glee or hated Glee, Criss performing "Teenage Dream" was one of the best moments of that six-year run, and his character of Blaine, who once memorably took a slushie to the face courtesy of Grant Gustin's nasty Sebastian Smythe, was a highlight. I was disappointed that this episode didn't feature much of Criss' musical talents; perhaps a return appearance may be in order so we can see more of what he can do.

Also fantastic are the musical veterans who join Barry and Kara in this world that they are placed in. As we saw on DC's Legends of Tomorrow earlier this season, any excuse to get Victor Garber singing is a good one, and the same thing goes for Jesse L. Martin whose Joe West was a musician on Earth-2 last year. John Barrowman is recast as a club owner here, and he and Jesse L. Martin's characters are rivals and enemies for reasons that will be revealed throughout the course of the episode. Obviously, both will sing. Also appearing and singing are Carlos Valdes -- if you haven't looked up him singing on YouTube, do so now -- and Supergirl's Jeremy Jordan. Some original music is performed for the episode including "Runnin' Home To You" sung by Grant Gustin and a fantastic number by Crazy Ex-Girlfriend's Rachel Bloom and Robot Chicken's Tom Root called "I'm Your Super Friend," performed by Gustin and Melissa Benoist with the characters looking like they're coming up with it on the fly. Fun stuff. "Runnin' Home To You," by the way, was written by the Oscar, Tony, and Emmy-nominated team of Benj Pasek and Justin Paul who recently got a lot of recognition for their song "Audition (The Fools Who Dream)" from La La Land. Their past credits also include Smash so you know they've got the TV-musical thing down pat. Hopefully these songs will be available on iTunes sooner rather than later.

Admittedly, some character motivations, especially considering the "Music Meister," don't make a whole lot of sense -- though, as is often pointed out in this musical realm, things don't often really make sense in musicals, do they? Since the music is catchy, I'm willing to give the episode a pass for that. Musicals make everything better, and "Duet" is an hour that ends with what will surely be one of the most talked-about scenes in DCTV history. We've been sworn to secrecy, but it does involve a song, and like that Buffy musical, it pushes forward the action for at least one of those shows. Maybe next time the team can bring in Oliver Queen and company so they can sort out their drama. 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.

The Flash: "Duet" airs Tuesday, March 21 on The CW.