[This is a review of Supergirl season 2, episode 12. There will be SPOILERS.]

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In the process of shifting from CBS to The CW for its second season, Supergirl underwent a number of changes, the most obvious of which being the departure of Calista Flockhart as Kara Danvers' boss/mentor Cat Grant. However, season 2 has also shown an increased focus on the alien population of Earth-38 with the first batch of episodes featuring the Girl of Steel battling the anti-alien organization Cadmus run by Lillian Luthor (Brenda Strong) - mother to, yes, that Lex Luthor, as well as Lena Luthor (Katie McGrath).

The familial connection between Lena and Lillian wasn't established until shortly before the midseason finale, but a great deal of Lena's arc in the first part of Supergirl season 2 focused on her attempting to distance herself from her family's hateful anti-alien beliefs. Although she eventually sided with Supergirl in the midseason finale, 'Medusa', Lena's loyalties and morality have been up for debate all season. Now, while Kara has complete faith in the goodness of Lena, the Luthor daughter's loyalties are tested once again in this week's episode.

In 'Luthors' -- written by Robert Rovner and Cindy Lichtman and directed by Tawnia McKiernan -- supervillain/Cadmus creation Metallo (Frederick Schmidt) breaks out of prison and frees Lillian. Thanks to her connection to her mother and overwhelming evidence, Lena is accused and arrested for helping Lillian escape. But, Kara believes her friend is innocent and sets out not only to re-capture Lillian but prove Lena's innocence as well.

The Only Two Luthors Left

As promised by its episode title, 'Luthors' pulls back the curtain on Lena and Lillian's relationship - as well as the mystery surrounding the tension between the two. Lena previously revealed to Kara that she was adopted, using it as a way to help distance herself from the negative connotations of the Luthor name. Plus, Lena also revealed that Lillian was often unkind to her while she was growing up, which understandably drove a wedge between the two. However, as we learn in this week's episode, Lena is more of a Luthor than Lillian.

Both Lena and Lillian have mentioned the more famous member of the family, but 'Luthors' introduces a young Lex Luthor on Supergirl in an opening flashback sequence to the night a young Lena was brought to live with them by the patriarch, Lionel. However, as Lillian reveals to her adoptive daughter later in the episode, Lena is actually a Luthor by blood since she's Lionel's daughter by way of an affair with another woman. The affair, Lena's later adoption when her birth mother died, and Lionel's guilt over the ordeal was what caused Lillian to distance herself from the girl. But, Lillian contends she still loves Lena - and they must stick together as "the only two Luthors left."

Of course, it's still not quite that simple. When Lillian escapes from police custody with the help of Metallo, she sends the Kryptonite-powered villain to retrieve Lena from jail since her daughter is framed for helping her escape. The breakout only makes Lena look guiltier, forcing her to depend on her mother - and Lillian uses that to her advantage when it's revealed she needs Lena's Luthor DNA to open a vault of anti-alien weapons created by Lex. All throughout the episode, Lena is portrayed as the victim - at least, to the viewer and to Kara, while the public believes she's in league with her mother. But, is Lena actually a victim, or is she a mastermind with an unclear endgame?

Since Lena's first appearance earlier in Supergirl season 2, she has been a compelling character with questionable intentions. 'Medusa' worked to subvert expectations as Lena was revealed to only be playing along with her mother's schemes in order to thwart them. Now, although viewers - and Kara - may fully believe Lena is unlike her family, that she is good, 'Luthors' manages to cast doubt yet again on her intentions. While much of the episode sees Lena fighting against her mother and enduring the prejudices of being a Luthor, her final scenes in the episode play on the expectations of the viewers, keeping them guessing about Lena's ultimate endgame - she's proven to be quite the chess player, after all.

That said, while the complexities of Lena's character certainly elevate this week's episode of Supergirl, her relationships both with Kara and Lillian are especially dynamic and compelling to watch. Whether or not Lena is a strategizer with an eye on the long game or a genuinely affected daughter, McGrath navigates both Lena's budding friendship with Kara and her tension-filled relationship with her mother with a dramatic weight that Supergirl has needed since Flockhart departed. While the sisterly dynamic between Kara and Alex has always been strong - and has been given more focus since the beginning of season 2 - it's also good to see Kara interact with another female character aside from her sister.

For now, Kara and Lena's friendship is sealed in donuts and flowers while Lena's relationship with Lillian seemingly ended with a Kryptonite-fueled explosion. Still, only time will tell whether Lena remains on the side of good - and it should provide for some compelling drama in the episodes of Supergirl season 2 to come.

Kara & Mon-El are Interrupted by... Mr. Mxyzptlk

Building off the threads established in previous episodes, 'Luthors' sees Kara admit she has feelings for Mon-El. After distancing herself from him in last week's episode, 'The Martian Chronicles' - while also focused on the White Martians' attack on M'gann M'orzz - Kara tries to return to some kind of normalcy with Mon-El, asking about his relationship with Eve Teschmacher (Andrea Brooks). But, though Mon-El plays off the burgeoning relationship as going fine, Kara learns from Eve that it was a non-starter after a bad first date - during which Mon-El could only talk about Kara.

The path that Kara and Mon-El have taken to this point has been contrived, incorporating romance cliches like Kara's realization of her feelings only after Mon-El had professed his own, and her jealousy of his supposed new relationship with Eve. The scene in 'Luthors' in which Kara confesses her feelings at least capitalizes on her struggle with relationships in the past - even if only in passing - and it's shot beautifully by McKiernan. Both Melissa Benoist and Chris Wood are charming in their own rights and they do their best to carry the scene, but it remains to be seen whether their individual charm will be able to translate to a real chemistry between their characters.

Of course, though it seemed the pair were headed for their first kiss, Mr. Mxyzptlk appears through a portal breach and professes his love for Kara. It's an unbelievable end to what could have been a boringly typical romance scene - and it sets up a fun, entertaining, and entirely out-there Valentine's Day episode in next week's 'Mr. & Mrs. Mxyzptlk'.

Next: The History of Lex Luthor’s Warsuit Explained

Supergirl continues Monday February 20 with 'Mr. & Mrs. Mxyzptlk' at 8pm on The CW.