Credit: Starz Original/BBC Worldwide Limited

Based on that globetrotting, apocalypse-flirting season finale of Torchwood, it’s hard to believe that this series began as just a Doctor Who spinoff on BBC Three about a black ops unit fighting aliens in apparently extraterrestrial-packed Cardiff, Wales. No, it still hasn’t come close to fulfilling its original mandate to give a more “adult” spin to the Who formula. Not by a mile. But what Torchwood still lacks in maturity it almost makes up with sheer expansiveness.

Take Series Four, subtitled “Miracle Day,” which wrapped up last night. It was in some respects a season-long deconstruction of most television series’ biggest conceit: that your main characters are never going to die, or at least have a much, much lower mortality rate than the general population. On the titular Miracle Day, not a single human being on the planet died. But then, none died on the day after, or the day after that, and so on, like some cancerous antipode to Children of Men’s sterility epidemic. After that non-Apocalypse Apocalypse, humanity became an immortal race of gods subjected to an increasingly crowded planet—except for those “Category One” individuals who should have died but haven’t and now linger on in some kind of limbo.

In a neat reversal, Capt. Jack Harkness (John Barrowman), himself a formerly immortal time traveler from the 51st century, now found he was not only mortal, but the only mortal man on the planet. The ten-episode arc was in itself a big question mark about storytelling: what kind of dramatic stakes exist when a character is no longer subject to mortality? Or rather, and perhaps more importantly, knowledge of his or her own mortality? Just as a life is made precious by our awareness of death, wouldn’t any story about characters never touched by the reality of death lack meaning? These are the kind of existential questions that I’m not sure Torchwood’s makers could have wrapped their geeky, pop-culture-soaked brains around in an earlier season.

And during “The Blood Line,” last night’s finale, Torchwood seemed on the verge of merging the epic and the intimate in a way no sci-fi series has accomplished since Lost. It opened with a long close-up of Gwen Cooper (Eve Myles) as she recounted a childhood memory of playing with her dad—now a comatose Category One—after he’d just been fired for stealing. “That’s my father,” she said. “The nicest man in the world. And today, I’m going to kill him.” That’s how you give your high-concept plot a human face!

Warning: Major Spoilers ahead!

Oh, if only more heartrending, character-driven moments like that had been on display last night. Torchwood’s always been pulled between smart sci-fi and snark sci-fi, and after that promising opening, “The Blood Line” seemed more interested in getting geeks to drool than think. As Jack, Gwen, and Rex tracked down The Blessings, two fleshy orifices—one in Buenos Aires, the other in Shanghai—that are the source of the immortality epidemic, and two of the worst special-effects set-pieces TV’s seen since Vaal on the original Star Trek (or at least that glowing, waterfall cave on Lost), any philosophical inklings vanished. Instead, a parade of geeky casting choices (Bill Pullman! John de Lancie! Francis Fisher!) and a subplot about a mole in a cocktail dress a la 24 took its place. Not to mention impenetrable technobabble. My favorite line? “It was as if something on this spot was calibrating a matrix subsisting alongside humankind….in harmony.”

I liked the idea that Harkness would have to die and give up all his blood to The Blessing in order to make people mortal again, though, and that dying would literally be the way for him to become immortal again. That led to one of the best moments of the finale, when Capt. Jack confronted Bill Pullman’s killer, Oswald, about how he’d deliberately made his life “small.” But instead of that being the climax, Harkness and Mekhi Pfifer’s Rex had to gush gobs of CGI blood to make mankind mortal again. Good sci-fi should be about inner space more than outer space…but not this kind of inner space. Still, it’s a bold series that builds a major arc not around saving lives but preserving the right to die.

PopWatchers, did you catch last night’s finale, and were you also a bit disappointed? Especially since Starz is not likely to renew it soon?