Inside the 'Flash' and 'Supergirl' Musical Crossover's Big Twist

'The Flash' and 'Supergirl' executive producers and stars break down the big twist at the end of the musical crossover.
Jack Rowand/The CW
'The Flash'

[This story contains spoilers from Monday's Supergirl episode "Star-Crossed" and Tuesday's The Flash installment "Duet."]

In the end, The CW's Supergirl musical crossover with The Flash was all about love, and the villain wasn't even a villain at all.

The crossover's mysterious "villain," the Music Meister (Darren Criss), arrived in National City during Monday's Supergirl to put Kara (Melissa Benoist) into a coma and then made his way to Central City for Tuesday's musical crossover with The Flash to do the same to Barry (Grant Gustin). As it turns out, it was because both superheroes were at a romantic crossroads: Kara had just broken up with Mon-El (Chris Wood) after learning he was lying about being the Prince of Daxam for the past nine months. Meanwhile, Barry called off his engagement to Iris (Candice Patton) after letting Savitar's (Andre Tricoteux) prophecy corrupt his reasons for proposing in the first place. When all was said and done, it turned out that the coma was actually a movie musical inside Barry and Kara's minds that was intended to help both couples get back together.

After the Music Meister told Iris and Mon-El that they needed to join Barry and Kara in the musical, Cisco (Carlos Valdes) vibed them in right as Barry and Kara were shot in a gang war in the 1920s-themed story. As both superheroes lay dying in the street, the couples realized their love for each other was more important than anything that stood in their way in the real world. Kara learned forgiveness, while Barry was able to put his worries about the future aside — all because their relationships were worth saving. Everyone made up and woke up in the real world as good as new and were shocked to see the Music Meister applauding their victory because he "believes in the good guys." 

"The lesson was love," Criss' charismatic character told the whole crew inside of STAR Labs. "Love is about letting yourself be saved. It's not just about saving other people, even if you are superheroes."

The reveal marks a big change from all the super-crossovers in the past, which have tended to feature some sort of formidable villain putting everyone's lives (or the fate of the world) at stake.

"At the end of the day, the best thing about the musical is that it doesn't exist outside the main narrative of what's going on, on both Supergirl and The Flash," The Flash and Supergirl executive producer Andrew Kreisberg tells The Hollywood Reporter. "Barry and Kara really needed to go on this journey because they both start this episode broken-hearted. This is an episode where they get their love back."

To hear Kreisberg tell it, the decision to make the Music Meister a hero instead of a villain just fit into the story. "At the end, that the cause of it would be somebody evil didn't feel right the more we worked on the plot of the episode," he says. "The idea that this person put them through their paces so they could get their love back on track ultimately seemed like a benevolent thing. We just thought that was so interesting. I mean, literally every show, every villain is evil. That somebody was doing something just to do some good struck us as very much the kind of thing a musical would do."

And it didn't hurt that the concept of the episode was a musical, either.

"There was a lot of darkness in our show this year and if you're going to do a musical and the Music Meister, it can't be dark. It has to be light," The Flash executive producer Todd Helbing tells THR. "It was the perfect 'villain' to lead us into something like this fantasy world. And we knew that we wanted to get to the proposal at the end, so what better way than to have Barry sing to Iris."

Fellow Flash exec producer (and Todd's brother) Aaron Helbing agrees. "The whole season has been about love," he tells THR. "Even going back to Flashpoint, that was all about Barry's love for his parents. It was more interesting [making the Music Meister a hero]. We always have villains. It's just so interesting when you have someone who sees two people that desperately need love in their hearts. It felt more satisfying to have a good guy rather than a villain. It was really important. Sometimes we do tend to go a little too dark. Like we did at the end of season two. It's just to remind people that it is a fun and light show and you still can watch it with your kids."

For her part, Supergirl star Benoist was relieved when she found out that the musical crossover villain came with a shocking twist. "He was just teaching them a lesson!" she tells THR with a laugh. "That's a great message to spread, that love is the answer and it supports everything and that's what you should fight for. Kara and Barry had obviously lost their way, and it was worth remembering that the people that they love are the most important things and why they fight for good is to keep the people that they love safe."

The actress noted that she loved the humor and ad-libs featured in the episode, which included a mini-Glee reunion with co-stars Gustin and guest player Criss. "It's only fitting for a musical comedy," Benoist says of the crossover's romantic ending. "And Darren was the perfect person to play that. He did an amazing job and was so charismatic and funny, and he just brings that positivity. It was the perfect twist for the setting."

Adds Gustin: "Everyone was asking about Darren and what kind of villain he is. It was cool that he just manipulated us. You never really see that on our show," he says. "It was a cool change of pace. It was unlike anything we've ever done or may ever do again. It was a nice break from all the melodrama that's happening all season. We really flipped that on its head and did the opposite and made it all about joy."

And Patton adds with a smile, "I don't think anyone wants to see Darren Criss as the villain. It was my first time working with him, and he was just so sweet that I was like, 'Yeah, I'm glad you're not a villain on our show.'"

Patton, meanwhile, notes that the episode will help Kara and Barry both get back on track. "Barry and Kara are the superheroes in the DC world who very much believe in love and are empowered by family and love," she tells THR. "We needed to see these two superheroes get back on track with that, so that they can be the superheroes that we know and love them to be."

By the end of the hour, both couples were stronger than ever, but Barry and Iris took the extra step and got engaged as he sang an original song, "Runnin' Home to You," to Iris as he proposed for a second time. "I'm like Barry where I think that music really helps elevate everything," Gustin says. "I've never wanted a music career because what I've always liked about music and musical theater is the storytelling aspect. And this song, it could borderline be like a theme song for Barry and Iris' relationship."

So does this mean that Barry and Iris' relationship problems are in the rearview mirror? "There will always be hurdles to get over, but it re-establishes the confidence that Barry has in their relationship and has always had," Gustin says. "It was missing there for, like, an episode, so it's nice to know that no matter what's going to happen, Iris is the love of Barry's life. We'll see them have to dodge some obstacles, but he's going to let their love carry them through."

Of course, there's still the looming deadline of speed god Savitar's prophecy about killing Iris to worry about, but at least Barry and Iris are together. "It's fair to say that they are firmly engaged and there are no more obstacles to deal with on that front," Patton says with a laugh. "With that being said, there is still Savitar and Iris' impending death. We won't be seeing wedding bells before the end of this season but ... if Iris survives, maybe next season."

Aaron Helbing confirms Patton's prediction that there won't be a West-Allen wedding this season, but promises that their romance will still be center stage for the rest of the season.

"They still have to figure out how to keep her alive and safe from Savitar, so that's really at the forefront moving forward of what's on their mind, now that they're as close of a couple as they can be," Aaron says. "So now how can the two of them, along with everyone at STAR Labs, figure out a way to save her?"

And Kara and Mon-El may not be at a wedding ring stage just yet, but their relationship is also back on track, thanks to the Music Meister's meddling ... at least, for now.

"It's beautiful that she found forgiveness," Benoist says. "It was hard for her to get past the fact that he didn't know how to tell her who he really was. But some Daxamites are coming and they're going to throw a wrench in things, so they're going to have another obstacle to face as a couple."

Supergirl airs Mondays at 8 p.m. ET/PT and The Flash airs Tuesdays at 8 p.m. on The CW. Keep track of all the super-shows in THR's Weekly DC TV Watch column every Friday morning.