Inside the 'Supergirl'/'The Flash' Crossover Twist and Its "Whedon-Esque" Moment

Supergirl Melissa Benoist and Grant Gustin still 1 - H 2016
Courtesy of CBS

[Warning: This story contains spoilers from Monday's The Flash crossover episode of Supergirl, "Worlds Finest."]

The Flash's Barry Allen (Grant Gustin) has left his mark on Supergirl.

The CW's Scarlet Speedster became fast friends with Kara Danvers (Melissa Benoist) on Monday's CBS-hosted cross-network crossover. The Flash's appearance served to help Supergirl get National City back on her side, and he became the catalyst for Kara finally taking her relationship with James Olsen (Mehcad Brooks) to the next level. After taking Barry's advice and planting a kiss on James, she was mortified when he failed to react to her. A few moments later, she realized he couldn't react, because Non's (Chris Vance) Myriad plan went into effect and turned all the humans in National City into mindless zombies.

"The repercussions from this episode are that she got the city back on her side and she obviously took a fledgling step with James," executive producer Andrew Kreisberg told reporters after a recent screening the crossover episode. "Those two events play heavily in the last two episodes [of Supergirl]."

So what is this mysterious Myriad plan that Astra (Laura Benanti) started before her death and Non has finished for her? Turning all the humans on Earth into brain-washed, mind-controlled slaves to the Kryptonians, starting with National City.

"You finally have found out what Myriad was. You're finally going to discover why Astra did it," says Kreisberg, who with Greg Berlanti exec produces both The Flash and Supergirl. "The idea of mind control, and as you'll hear in subsequent episodes, you'll start to get very cogent arguments on the bad guys' side for why Myriad is the way to go. We always love it when the bad guys have a point. They're leaving out the part about killing a whole lot of people or you losing your free will, but next week Non actually gives a speech where he talks about, 'What has your free will gotten you? It's gotten you a planet full of reality TV shows, politicians who can't stand each other and all of you are sitting around, standing by as global warming is coming to destroy your planet. What if everyone was working together? Wouldn't that be better?' Obviously that's horrible that you're losing your free will, but he has a point of view that you could argue."

But Kara won't be alone when she tries to stop Non's plan going forward.

"Kara has a couple of surprising players that you wouldn't expect to be the two people who are completely unaffected by Myriad to help her," Kreisberg says.

One ally might be Kara's sister Alex (Chyler Leigh), despite being on the run from the government with Hank/J'onn J'onzz (David Harewood).

"She is on a mission but Myriad taking over the entirety of National City is going to put into question which mission she should be pursuing," Kreisberg says. "Obviously she knows her father is alive and out there but the entirety of National City has been taken over and there's going to be some discussions with Hank in the subsequent episodes about which danger is more immediate and pressing."

Supergirl will return to Alex and Hank's story in the next episode, when "we see them on the run in a very comical way." "I think it's surprising as much as comical," Berlanti says. "It's cool."

As for why the showrunners decided to have Kara make the first move on James instead of the other way around, Kreisberg joked that "the show's called Supergirl."

"She's the one who got the advice this week," Kreisberg says. "Barry's advice about when to go slowly and when to move fast really resonated with her. She finally realized too that they've had so many fits and starts throughout the course of the year and so much of it was because one or the other of them didn't stop talking and just act. The idea that just as they kiss, Myriad takes over, and doing the gag of, 'Was it good? Was it too good? Was it not good?' Poor Kara's horrible reaction after finally making the first move and he's turned into a zombie just felt like the best kind of [Joss] Whedon-esque pathos."

Kreisberg and Berlanti also revealed that Bizarro almost made an appearance in the crossover to team up with villains Livewire (Brit Morgan) and Silver Banshee/Siobhan Smythe (Italia Ricci), but decided against it for budgetary reasons. And this is the last viewers will see of Silver Banshee this season, but the Berlanti "would love to" have Ricci back for season two.

As for that comment Cat Grant (Calista Flockhart) shot at Kara, Barry, James and Winn (Jeremy Jordan), calling them an attractive cast of a CW show? 

"That was the most fun aspect of the crossovers for me as a writer, getting to put in those real meta kinds of jokes," Kreisberg says with a laugh. "That was actually one of the earliest jokes we had written for it. It just cracked me up."

Supergirl airs Mondays at 8 p.m. on CBS and The Flash airs Tuesdays at 8 p.m. on The CW.