The Flash season 3 has been a more serious season than most, primarily dealing with heavy issues relating to Barry's grief, fear, and over reliance on time travel to fix his problems. Recent episodes have seen Savitar return and Wally pay the price for it, all the while the threat of Iris' murder still looms in the future.

Tonight's episode, however, promises to cast aside those worries in favor of some good, old-fashioned song and dance numbers. 'Duet' -- written by Greg Berlanti, Andrew Kreisberg, Aaron Helbing and Todd Helbing, directed by Dermott Downs -- is the much anticipated Flash/Supergirl musical crossover, bringing together cast members from both shows as well as a few of the Arrowverse's other musically-inclined talent.

The circumstances for this crossover are unusual: the Music Meister, a villain with the ability to trap people inside their own fantasies, snatches away both Supergirl and The Flash, forcing them to sing and dance for his own amusement. Unable to escape and without their superpowers, Kara and Barry must sing to survive, all the while rubbing elbows with 1940s musical versions of their closest friends and family. Meanwhile, Mon-El, J'onn J'onzz, and the rest of Team Flash work together, hoping to discover some way of freeing them, but it seems the only way out is to go on with the show.

The Music Meister

Supergirl Flash Crossover Duet Music Meister Explained

Debuting on the Batman: The Brave and the Bold cartoon series and appearing in only one episode, the Music Meister has gained something of a cult status among fans thanks to the episode's catchy tunes and splendid Neil Patrick Harris performance. Despite that brief appearance, the Music Meister transitions into the Arrowverse with 'Duet', delightfully portrayed by Grant Gustin and Melissa Benoist's Glee co-star, Darren Criss.

However, any connection with the original Music Meister is in name only, with much of tonight's musicality stemming from its main stars rather than him. This isn't to suggest he doesn't sing or dance (he does and it's wonderful), but unlike the animated Music Meister, his powers in no way originate in song. There's no hypnotism or mind control created by the pitch of his voice, and even his name is more a result of Barry and Kara's predicament than it is his character.

The Music Meister appears omnipotent and the episode never really explains if he's alien or god or something else entirely. Not only can he trap people within their own minds, but he can travel between realms and steal superpowers, suggesting whatever he is, it's unbelievably powerful. And though his scheme in 'Duet' involves stealing both Supergirl and The Flash's powers, in the end he's revealed to have actually been teaching them a lesson about love. So he's a benevolent, omnipotent, trickster-type character, which actually makes him much more like a character from the fifth dimension, Mr. Mxyzptlk -- who Supergirl only recently faced, so it's odd that neither Mon-El or J'onn J'onzz suggest this.

Regardless, the Music Meister is a fun addition, basically coming on the scene just to allow for our characters to cut loose and learn to love the one they're with. He simply fades away at the episode's end, so there's reason to think he could return. And if he does, since they've cut the musical side of his origin, another visit wouldn't necessarily guarantee a musical episode; The Flash (or any Arrowvese show for that matter) could include his character to have some fun in any genre.

Things Really Are Easier In Musicals

Supergirl The Flash Duet Barry Allen Kara Danvers

As it turns out, the explanation given for 'Duet's musical scenarios is that both Kara and Barry hold a deep love of musicals, so when "whammied" by the Music Meister, they imagine for themselves a world right out of a 1940s musical. The reason they've been "whammied", as the Music Meister explains it, is that he saw two people with broken hearts and decided to help them. Was that really any of his business? No, but that's what makes him an unwelcomed presence -- well, that and his threatening of both Kara and Barry's lives, since it's pretty clear they will die if they aren't saved by their true loves.

And in that sense, while 'Duet' is most certainly a musical, referencing as many of the genre's tropes as possible, there's also a real fairy tale vibe to this episode. In the end, Iris and Mon-El are only able to free Barry and Kara by enacting what looks an awful lot like True Love's Kiss. This, of course, only comes after Barry learns to just love Iris and face the future together, and Kara learns to let herself get saved every once and a while, forgiving Mon-El for having lied to her. In one fell swoop, both The Flash and Supergirl have their protagonists resolve their relationship problems, which is great, freeing up precious screen time for more pressing matters, like Savitar and Cadmus. Hey, things really are easier in musicals.

Everything's Better In Song

Victor Garber Jesse L Martin The Flash Duet

'Duet' dealt very little with either Supergirl of The Flash's major narratives (outside of the love drama), which isn't too surprising since the appeal of this episode was to see its stars sing and dance. Well, sing and dance they did and it was just lovely, making for a charming episode that was clearly a lot of fun for those lucky enough to be involved. Benoist's rendition of "Moonriver" was sublime, and her and Gustin tapping away during "Super Friends" was a treat. These two really do share great chemistry, and whether singing or not, there needs to be more Flash/Supergirl crossovers.

Both Carlos Valdes and Jeremy Jordan also got to show off their pipes, practically begging for more reasons to get these two singing (a karaoke night, maybe?), but the real "wow" moment of 'Duet' must go to Jesse L. Martin, Victor Garber, and John Barrowman for their rendition of "More I Cannot Wish You" from Guys and Dolls. All three are musical veterans, so it's no secret they all sing marvelously, but with the added emotion of the scenes and the way in which their voices blend, their number was simply the best.

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'Duet' was a silly episode and certainly one that will irritate those who just abhor musical theater. But for anyone else, it was a hoot. Barry and Kara had a chance to return to their more light-hearted selves, free of their serious burdens, and both shows patched up their main couples in an efficient manner. The real draw was getting to hear cast members sing and watch them dance, which to be fair, has been done before and even better by shows like Buffy the Vampire Slayer, but 'Duet' was still a most enjoyable distraction. And good timing, too, because with only a handful of episode left, both Supergirl and The Flash are about to get more grim.

The Flash continues next Tuesday with 'Abra Kadabra' @8pm on The CW.