Supergirl ending spoilers follow.
Supergirl has the distinction of being one of the relatively few comic book movies that could accurately be described as a direct adaptation. We're used to Marvel and DC happily patchworking together a few names and narrative beats – take the way Avengers: Infinity War borrowed Thanos and his powerful Gems from Jim Starlin, George Pérez and Ron Lim's The Infinity Gauntlet series, but discarded almost every other element.
Craig Gillespie's Supergirl, however, sticks comparatively close to the plot of Tom King and Bilquis Evely's 2021 miniseries Supergirl: Woman of Tomorrow. We meet a grief-stricken Kara Zor-El aka Supergirl (Milly Alcock) drowning her troubles with booze in a remote bar on a remote planet with a red sun – she, like her fellow Kryptonians, draws her strength and abilities from the yellow sun, so she's gone to the only place she can actually get drunk.
While her cousin Kal-El, aka Superman (David Corenswet), was sent away from their home planet of Krypton as an infant, Kara remained. She grew up there. She saw its destruction first-hand. It's hard for her to really care about anything much at all now.
That cynical, calcified worldview is finally challenged when a young girl, Ruthye Marye Knoll (Eve Ridley), attempts to enlist her help in avenging the murder of her family at the hands of the piratical Krem of the Yellow Hills (Matthias Schoenaerts).
Yet, there's one major change to the source material that's already become a point of contention with fans – and it's to do with how Kara chooses to deal with Krem when she eventually catches up with him (it's probably worth pointing out here he also poisoned her dog Krypto).
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Ruthye, in both versions, wants him dead. But in the comic, Kara reminds her of her heroic vow not to kill, instead choosing to banish him to the Phantom Zone, where he's stuck in a state of suspension for the next 300 years. That's enough time for him to learn a few lessons, and he returns repentant.
In the movie, Kara convinces Ruthye not to kill him – she's an innocent and shouldn't have to carry the burden of taking a life – before waiting until the kid's out of earshot and promptly stabbing Krem to death.
For many a comic book fan, the question of whether their favourite hero has a no-kill rule or not isn't something to be messed with. Zack Snyder learned the hard way with his trigger-happy Batman and Superman.
But there's much less of a consensus in the comics of who, exactly, Kara Zor-El is. When first introduced in the Silver Age in 1959, she was an optimistic, moralistic mirror of Superman, yet subsequent portrayals have shown her struggling more openly with the loss of her people. She can be a little skeptical of Earth, at times.
And, on rare and very specific occasions, those darker emotions have led her to kill. She's taken out Lobo (portrayed by Jason Momoa in the movie). Twice.
So, she's not entirely squeaky clean.
Woman of Tomorrow is a standalone series. It created and completed a narrative arc for its Kara. In May 2025, Sophie Campbell took on the character and returned her to the brighter realm of the Silver and Bronze Age comics, though not without the occasional angst.
Meanwhile, Kara's solo DCU adventure ends with her return to Earth, where she tells Superman that she plans to stick around for a while, finally at peace with the idea that she has a family and a home, even if it's not the one she lost.
She'll return next year in James Gunn's Man of Tomorrow, a sequel to his Superman movie. It's clear from the few scenes she's shared with Corenswet on screen already that the pair play beautifully against each other, and placing her as a moral counterpoint to him when it comes to violence immediately ensures that she can remain at the heart of the conflict, with no risk of her being reduced to the role of supportive echo.
There are certainly other characters in DC that could do the same job – Wonder Woman will kill when necessary, which doesn't always go down well with her fellow Justice League members, and Gunn's current Justice Gang have demonstrated a somewhat more reckless attitude towards life – but there's something more complex and poignant about the pushback coming from someone in his own family.
And, from the little we've seen of Gunn's vision for the DCU, as the co-chair of DC Studios, there's a clear interest in the idea of how much someone's circumstances dictate their worldview. Think of the reveal about Superman's parents. Or the idea that Peacemaker's life would have been very different if he hadn't grown up with an abusive father.
As Kara says, she had to witness the world's brutality. Kal-El was shielded from it: "He sees the good in everyone; I see the truth." In fact, one of the flaws of Gillespie's movie is that it barely scratches the surface of that statement. We never really get the full picture of Kara's own history of violence.
That's why that climactic kill matters. There's so much more of Kara's story left to tell.
Supergirl is out now in cinemas.
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