20 years ago, Lillian Luthor was playing a rather severe game of chess with her son (and the fans do a little dance overseeing Lex in any context that isn't freaking Batman v Superman). The door opens, and Lionel Luthor walks in with a little girl whose presence immediately sets Lillian's teeth on edge. Clearly, we're seeing the moment when Lena was brought home as an adopted child, and Lillian was not on board with this plan.
In the present day, the gang is gathered at the alien bar (does this place have a name?), where Alex has asked them to come meet her new paramour for official friend-troductions. Winn and James are talking about "who's this new guy," and "what do you know about him" in such a way that you can tell the director told them, "Really be sure to emphasize all the gendered words so the audience gets the joke," but come on, give us a little credit.
Alex wanders over with Maggie, and there's the requisite stammering from Winn and James, followed by some sweet moments: J'onn acknowledges that this is no surprise to him, because he's a telepath, but he would never have interfered in her journey of self-discovery by telling her things she didn't yet understand about herself; Mon-El is adorably perplexed by the notion that two women loving each other is a controversial concept on Earth.
The trial of Lillian Luthor is the big news story of the week, and Lena has given damning testimony against her mother. Next up on the stand is Metallo, and the night before he heads to court, he gets a sketchy delivery through prison mail: Kryptonite! On the witness stand, he rants xenophobically for a while, then starts blasting the place and escapes with Lillian.
Sudden video evidence is sent to the authorities to implicate Lena as Metallo's Kryptonite Fairy. She insists it's not true, and Kara believes her...but no one else. She's off to jail.
At the Catco offices, Kara and James have yet another contentious moment about his being Guardian, because Kara's stridently declaring that she believes in Lena because of friendship, and James reasonably points out how friendship doesn't seem to help her believe in him. Irritation inspires him to stake out Lena's cell block in his Guardian gear and take on Metallo when he comes to break her out. Metallo wins this fight, unsurprisingly.
Lillian puts on a hard sell with Lena, trying to convince her that there is real maternal affection beneath all the cold, manipulative, stone cold bitch behavior. She finally tells Lena the truth of her parentage: Lena is not exactly adopted; she's Lionel's illegitimate daughter from an extramarital affair.
Of course, the real reason Lillian wants Lena around is this DNA connection; Lillian only married into the Luthor name, but there's a biological lock she needs a true Luthor to open. Lena is forced to provide her blood for the lock, and it opens a vault of Lex's anti-alien toys. Something in a little metal box seems to be what Lillian always wanted for Christmas...share your theories on what it is in the comments!
Back at the DEO, they've located Metallo's radiation signature on GPS and determined that his artificial Kryptonite heart is unstable and about to blow. Kara zooms off to save Lena, and J'onn follows as fast as he can, because he's not vulnerable to Kryptonite and therefore way better suited to this mission.
Lillian and Hank Henshaw escape. Kara and J'onn rescue Lena and get out just in time. Most of Lex's toys are presumably destroyed, but Lillian did seem satisfied with what she picked up.
In the end, Lena is vindicated, and she thanks Kara for believing in her. All seems well...until Lena is alone and her expression darkens ominously.
In other news, Kara figures out that Mon-El isn't really dating that chick from Catco, and she finally admits to him that she might maybe kinda sorta um, well...and then there's almost a kiss, but...OMG, it's Mr. Mxyzptlk!!! I love when they take us this deep in the DC mythology. Next week is going to be a blast.
I give this episode an 8. My favorite detail may be the mention of Clark and Lex being best friends for years--this clearly references the wonderful storyline of Smallville, as opposed to the trash heap of Batman v Superman. Keep us in the Smallville universe, please, and I'll be happy.