Thwarted not once, but twice in the middle of fascinating character arcs on science fiction TV shows, Summer Glau remains a should be/would be superstar. Her portrayal of the psychologically damaged child prodigy River Tam in Joss Whedon’s Firefly (and Serenity) chills, touches, and ultimately explodes in balletic, kick-ass style. The writing hints and teases throughout the clipped series, sparking moments of intense vulnerability against WTF just happened crazy action beats. We want to throw an arm around her to keep her safe, but we’re not too sure what she’s gonna do with it. Like a wounded jaguar, she’s lithe and needy and liable to tear you to shreds without warning.

I wasn’t sure what to make of Summer in those first couple of episodes. She seemed too jittery, too blank as a performer, playing a cliched damaged goods girl who pouted a lot and didn’t add anything to the chemistry of the crew. But Simon, her devoted brother, saw something in her character that we didn’t, and it’s through him that River tranforms before our eyes into a lethal weapon with a fiercely loyal heart. She doesn’t always know what triggers her conditioned violent outbursts, but Simon is there to remind her who she really is, under the layers of neural rewiring.

When she goes ballistic to save their lives in Serenity, it’s a bittersweet moment for fans in that River is finally able to master her awesome potential and use it for good, but has been robbed of the several series of emotional build-up Whedon would (presumably) have given her. And of course any follow-up story arcs we’ll never get to see.

Science fiction is a perfect showcase for action heroines because when dreaming up future scenarios, you can easily throw gender bias out the window. For contemporary and especially historical stories, your action heroine’s automatically an exception to the norm of male-dominated heroics, and fairly or unfairly, that frames who she is, how the world perceives her. Call it reality tax.

In modern science fiction TV, it’s often a given that gender equality extends to every walk of life: from Zoe and Kaylee in Firefly to Starbuck in Battlestar: Galactica to Tasha Yar in Star Trek: The Next Generation, a woman can be anything she wants to be, in equal competition with her male colleagues. Mostly. “Reality” there has evolved, and viewers (or readers) will far more readily accept a powerful action woman without a relapse to conditioned cries of “Hey, wait a minute! That could never happen!” When River gets full-on medieval, we’re not shocked because she’s female, it’s because she’s a doe-eyed teenaged girl we’re used to seeing cowering under a blanket in the corner. That dichotomy of vulnerability and lethality is fascinating because (particularly male) viewers are on uncertain ground. It’s the femme fatale idea taken to extremes. Given a few more seasons, I think we’d be talking about a phenomenal action heroine rather than a quirky, interesting one.

As River, Summer showed she could play icy as well as anyone, but she could also be warm and charming when she revealed her close bond with her brother.

That contrast would come to define her next major science fiction role, too, and it’s probably the secret to her appeal. Summer Glau is one of the sexiest women I’ve ever seen, but I didn’t realise that until I watched her in Terminator: The Sarah Connor Chronicles.

Cameron Phillips is a cyborg sent back to protect John Connor, future saviour of mankind. She’s supposed to resemble a typical high school girl, only she has striking exotic looks, a stunning ballerina’s figure and an impossibly beautiful smile. The writers use the story of the first two Terminator films, but they fashion an interesting family dynamic here involving John, his warrior mother, Sarah, and this potently female robot protector who isn’t exactly Mom’s ideal bodyguard for her rebellious teenaged son.

There’s a fascinating is she/isn’t she sexuality at work whenever John spends time alone with Cameron. He’s clearly attracted, but understandably keeps his distance, while she maintains her poker face yet occasionally lets slip a hint of a deeper connection. Sarah seems aware of this unusual chemistry between them, and the only reason she doesn’t send the bitch packing is because, well, Cameron’s even more deadly in a fight than River Tam. John’s odds of survival increase a hundredfold when she’s around.

Until you get to the girl-next-door—her real-life persona—there’s something superficially cold and untouchable about Summer. The big eyes, the slightly pouty face, the not-quite-sure-where-she-comes-from looks: it’s not a stretch to imagine TV viewers being unsure of what to make of her. Sarah isn’t sure either. Neither is John. But that winsome vulnerability, so overt in River Tam, operates much more subtly here. Cameron might be an all-but-indestructible machine, but she’s also still the high school girl John had a crush on in episode one, capable of a winning smile and warm companionship, however much they’re acted. When she’s getting pummelled by other robots, we want to jump in and protect her (good luck there). When she’s poker-faced and spouting protocols in place of conversation, we wanther to wish upon a star and become a real live girl for John.

That’s why robots fascinate us in fiction. They’re almost human, and we have a problem with the disconnect, with the impossibility of one actually becoming human. We’re ultimately denied the fairytale happy ending every time, no matter how much we want one.

That’s where I wanted The Sarah Connor Chronicles to go with Cameron. To heighten the emotional dynamic between her and John, to create a unique love frisson that ended with a powerful climax, a la Arnie’s tearful farewell at the end of Terminator 2. Maybe it would have. But after two brilliant seasons—particularly the second—the show was cancelled. Summer never got to fully realise the sprinkled secrets of her cyborg’s character. She was excellent in the role, for all the reasons I’ve mentioned, and a lot more interesting than Kristanna Loken’s T-X in the underrated Terminator 3. Given time, I feel she could have gone on to portray a truly complex action heroine, sparking off John Connor in all sorts of unpredictable ways, like she could have done as River Tam with the Firefly crew.

Sooner or later she’ll get that chance. She has to.

Summer’s only just beginning.

Check out this interview with Summer for the LA Times.

And if you enjoyed this article, further reading on sci-fi heroines here at Contact: Infinite Futures includes Milla vs the World and my rundown of the Top 10 SF Movie Heroines.

Robert Appleton is an Award-winning author of science fiction, steampunk, and historical fiction. He currently lives in Northwest England.