The origin of Kryptonite is one of the more bandied-about bits of Superman trivia. It wasn't actually introduced in the comic books where Superman and his kin first appeared, but rather in a radio show in 1943, a full five years after Superman had been created. Kryptonite was a classic Silver Age device, equal parts contrivance and poetry — the great weakness of Superman, Supergirl, and any other Kryptonian was nothing other than radioactive fragments of the home they lost, now toxic to them.
More than anything, though, Kryptonite illustrates the fluid nature of comic-book storytelling. It's a clear example of how the idea of a "definitive" version of a comic-book character is kind of a sham; the "true" version of Superman is actually a composite. The traits that stuck around form the cores of the characters we follow — not across published history, but across decades of complex and often nonsensical continuity. Supergirl innately understands this, playing fast and loose with some details (the DEO, Hank Henshaw) while bringing in silly old iconography (Jimmy Olsen's signal watch) in a charming way that makes sense within this new context. It's the gestalt of Supergirl that matters, the whole that is greater than the sum of its parts.
But where those parts come from can still be fascinating. Red Kryptonite, the strain that turns Kara bad and features prominently in this episode, is most clearly descended from Smallville, of all places, with a dash of Superman III. The end result is a classic Jekyll-and-Hyde scenario, in which the hero's selfish nature takes over and they become destructive and unrestrained. This often comes with terrible consequences, but it sure is fun to watch.
For Kara, who is exposed to Red Kryptonite after saving people from a burning building, this means she first starts to take after Cat Grant. She comes to work wearing the loudest pair of heels in her wardrobe and a slinky striped dress with a peekaboo midriff, promptly out-Siobhaning Siobhan, and impressing Cat with her brazen behavior.
At the DEO, she's bored by Hank's lecture about the rogue alien they're about to apprehend, an ugly one-eyed bruiser known as a K'Hund. (She sums up the briefing as "Kick. Alien. Ass.") This is where things become a problem — although she easily, almost nonchalantly, trounces the K'Hund, she decides to let him get away, merely because he's not strong enough to consider a threat.
Hank is furious at her nonchalance, but it turns out Kara is harboring resentment towards him as well. She's chafing under the expectation that she follow orders and put her life on the line. Hank could be using his powers, too. Why doesn't he? Alex and Hank are taken aback by Kara's blowup, but given her comment about how she has to go off to "another job that underappreciates her," things are about to get pretty nasty.
Totally uninhibited now, Kara takes Cat's personal elevator, gets Siobhan fired by ratting her attempt to give a scoop away to The Daily Planet, and then invites Winn and James to go clubbing with her. At the club, she dials it up to 11. She makes a beeline to the dance floor with James, then says she can finally have what she wants, what "the poor man's Lois Lane was too idiotic to keep."
James is understandably insulted and actually hurt by Kara's grip when he tries to pull away, but a call from Cat Grant asking to see Supergirl cuts any confrontation short. Winn and James have seen enough to know something is very wrong.
One of the more surprising things about Supergirl is how often it centers its moral compass on Cat Grant. This is one of those times. "You don't get to be a normal person," Cat tells Supergirl, after Kara expresses resentment at her branding as a girl scout. Video footage has been found of Kara letting the K'Hund go (it's what got Siobhan fired) and Cat is reminding her that she has an image to maintain. "You're a superhero. You get to represent all the goodness in the world."
Kara is done with all that, though. "Get used to the flames," she says. "I quit."
Then she lectures Cat about power before throwing her off the building, then catching her moments before she hits the ground just to make a point.
By now, Winn and James have gone to the DEO to talk to Alex and Hank about what's going on with Kara — and they're joined by the actual person responsible, Max Lord. Turns out he was trying to make his own synthetic Kryptonite in order to prepare a trap for Non, but he couldn't quite get it right. Evil Kara is an unintended consequence, and he vows to work on a cure for her.
I'm far more entertained by pragmatic Max Lord than I am mustache-twirly Max Lord, so I'm curious to see where he falls on the friend/foe continuum in the end. Either way, he has one of the night's funniest lines, when he casually mentions he witnessed Kara tossing Cat off of a building.
Winn: "SHE KILLED CAT GRANT?!"
Max: "Noooo, Cat's fine. She has nine lives."
Grade-A snark and a terrible pun. Supergirl, you are too generous.
However, that attack comes with repercussions: Cat takes the chance to publicly denounce Supergirl as a threat to National City, and National City listens.
Kara doesn't seem to mind. She dons a badass new catsuit that's very Black Widow, refusing to heed her sister's warnings about what the Red K is doing to her. At this point, Kara is in the throes of full-blown megalomania, demanding awe and worship from National City, even re-enacting the scene from Superman III where that movie's Asshole Superman uses peanuts to shatter bottles of booze just for laughs.
At this point, Hank and Alex show up with the DEO to stop Kara, who is now totally out of control. Alex has Max Lord's cure-ray but isn't able to use it … because it looks like Kara is ready to kill her.
Then Hank breaks his one rule and finally turns into his Martian form, taking Kara on in a REALLY COOL FIGHT SCENE. Unfortunately, this means people know about J'onn J'onzz now, as the fight is captured on countless smartphones.
J'onn is able to subdue Kara long enough for Alex to use the cure on her. Instead of fleeing, however, J'onn reverts to human form and submits to the authorities that he once commanded.
Now it's up to Kara to pick up the mess she made: Hank is now a prisoner of the DEO, Alex's arm is broken, National City does not trust her, and James demands that she give him some space, clearly troubled by the glimpse of meanness that could still be hiding inside her.
The only person she can face right now is Cat Grant, someone who knows all about reputation and setbacks, someone who can tell her that everything isn't going to be okay but it can be fixed.
It won't be easy, though.
- Winn, you dog. Early in the episode, Winn is missing around the office. Kara goes looking for him, suspecting that he's locked in a supply closet. She's right, but it's by choice — he's totally getting it on with Siobhan. "It looks wrong, and it feels wrong," he half-explains, half-pleads, hilariously. "Except for when it's happening, and then it's … " Kara doesn't want to hear the rest.
- Role models. Two of tonight's best scenes involve a schoolgirl named Laura. In the intro, she's being bullied by her classmates for wearing a homemade Supergirl outfit, but luckily for her, Supergirl is nearby and arrives to stick up for her. It's a charming, heartwarming scene that's Supergirl at its best. The mood then flips after Cat denounces Supergirl over the air, and we briefly see Laura throwing her adorable outfit away and it's so sad.
- Senator Miranda Crane returns. Tawny Cypress pays another brief visit to National City as the former xenophobic senator from "Strange Visitor From Another World." In another consequence of Kara's bad-girl turn, Crane does not take kindly to J'onn assuming the identity of Hank Henshaw, and it looks like the future of the DEO is on shaky ground.
- The Eddie Brock-ening of Siobhan Smythe. We almost certainly haven't seen the last of Siobhan, who now has every reason to want revenge on Kara. Her ousting even has shades of the Spider-Man villain Venom, which makes perfect sense. In the comic books, Siobhan Smythe is the alter ego of the villain Silver Banshee … whom we might see along with a certain other very special guest in two weeks. I'm so excited about this.