Synopsis: After Kara finds herself in double trouble when both a new and old enemy team up to come after Supergirl AND Kara Danvers, she gets some surprise backup from The Fastest Man Alive.
Or, as I like to call it, Nerds: The Episode. In what is probably the most meant-to-be crossover of all time, despite being on different networks, The Flash comes to National City and teams up with Supergirl.
After Siobhan’s superpowers inexplicably manifested themselves to stop her from falling to her death last week, Winn takes her to the DEO where they determine that she’s human, and her powers cannot be explained, meaning she must have been born with them. Furious, she storms out, but not before stopping to overhear Lucy talking to Livewire in her cell, and see what her powers can do.
Siobhan goes to visit her aunt, who reveals that the women in their family are, for lack of a better word, Banshees. They’re destined to be unlikable, and when someone wrongs them, they developing an all-consuming need to destroy things with their superhuman scream, until the object of their anger is killed. For Siobhan, this would be Kara.
Siobhan attacks Kara at CatCo, and throws her out of a window. Kara falls, but before she can stop herself, she’s rescued by The Flash! Barry Allen himself has accidentally run too fast, and crossed into another alternate earth. And just in time, as Kara is about to be in over her head.
Kara and Barry are honestly the most lighthearted, dorky, affectionate, genuine, and completely delightful superhero duo imaginable. He nerds out over her spaceship, she nerds out over his speed, and the concept of infinite earths, they eat donuts together and fight side by side and risk their lives for each other without hesitation.
Winn, also a nerd, loves Barry too. James however, is less than thrilled at how quickly and easily Kara takes to Barry, and how much they have in common. His jealously does not go unnoticed by Lucy or Cat, who tell him to make a move already, but his curmudgeonly, deadpan disinterest in the sunshiney, oblivious Barry might have been the best part of the episode.
Defeated, Siobhan decides to break Livewire out of the DEO, because they want revenge on Cat Grant and Kara Danvers respectively, but both are under the protection of Supergirl, who can’t be taken on alone. Luckily, Barry just happens to be in National City, and together they come up with a plan to take down both Livewire, and the newly-anointed Silver Banshee.
In the process, Kara manages to win back at least some of the city’s trust, that she lost after her actions were affected by Red Kryptonite, by throwing herself in the path of Livewire’s electricity beams to keep her from taking down a police helicopter. When she crashes to the ground and Livewire comes in for the kill, the bystanders gather around Kara protectively while the firemen spray Livewire with water and incapacitate her.
The fact that Barry was straight-up trapped in an alternate earth with no way home was the driving force behind his presence in the episode, and his agreement to help Kara in the first place, but it went largely unexplored and was resolved instantaneously. This meant a great scene where Kara and Barry race at full speed in tandem until she throws him into empty air, just like, hoping it will be fast enough for him to pass back between worlds though, so I’m cool with it. And he does. Supposedly.
In the end, Kara finally, adorably, makes her move on James. She rambles for a little bit before just grabbing him and kissing him. When she pulls away, he doesn’t react. At all. He stands there, completely stone-faced, staring into space while she freaks out about misreading his signals. Without even blinking, he turns and walks out of her apartment like a robot. She chases after him, and finds that everyone else in town is doing the same.
It appears Non has finally activated the Myriad device, and is using it to control the entire population of National City, and eventually, the world.
This is super (pun INTENDED) compelling given the timing, with Kara and James finally coming together, Barry having just left and Hank and Alex on the run. Kara, being alien and immune to Myriad, is now – quite literally – the only person in National City who can do anything about it.