Click here to read about real-life crime-fighting in Sherlock Holmes-era London.

What makes this Sherlock different from all the other Holmeses? The Sherlock that returns to Masterpiece Mystery for a second season on Sunday (PBS, 9 p.m. ET) is modern, witty, and served up with a cheeky wink. (It’s also poised for an American breakout as its stars achieve more mainstream fame.) Played by Benedict Cumberbatch, all cheekbones and billowing Belstaff coat, Sherlock’s Sherlock’s a fast-talking, giggle-inducing tease. Without ever mentioning Arthur Conan Doyle or any of the earlier incarnations of Holmes, the series plays the classic accessories and tics—the wardrobe, the bad habits, the maddening lack of impulse control—for amusement: In 21st-century London, there is no way to wear a deerstalker unironically, and Sherlock doesn’t even try.

But he is also a conundrum, and many viewers spent the first season, which first aired here in 2010, trying to puzzle out who he truly is. Sherlock may be set in the present day, but Sherlock can be doggedly old-fashioned: Though he always keeps an iPhone close at hand, he prefers to stare into a microscope and visit the “mind palace” inside his head. He is a showoff, yet he keeps his most impressive feats of detection to himself. He’s a Johnny-no-mates nonetheless willing to sacrifice everything for the handful of people he cares about. And he is an asexual manipulator who somehow seduces everyone he meets. Is he a sociopath or on the side of the angels? Or, as the show suggests at times, both? Earlier this week, I asked Cumberbatch and Steven Moffat, the show’s co-creator, to help me distinguish the red herrings from the reliable clues to Sherlock’s character.

In the first of this season’s three 90-minute episodes—self-contained movies, really—Sherlock tangles with Irene Adler, a crafty dominatrix being chased by American spies and British royals. Sherlock is impervious to her charms—she can’t even fluster him by entering the room naked. Does his apparent lack of interest in the sins of the flesh mean that Sherlock is asexual? Not according to Moffat, who is best known to U.S. audiences for his work as a writer and now show-runner for Doctor Who. Holmes has simply suppressed certain appetites for the sake of his calling as a consulting detective: “All that sex lark? That doesn’t matter. All that emotion? That gets in the way,” Moffat says. “He cuts through all that to what he wants, which is to be the very, very best at what he does.”

But what about his manners? As with his distant cousin Gregory House, Sherlock’s sense of his own superiority makes him careless with other people’s feelings, unable to mute his powers even when his observations hurt. When a female guest arrives at a Christmas gathering at 221B Baker Street in the season premiere, Sherlock announces that a perfectly wrapped gift tucked away in her bag is clearly an attempt at seduction—embarrassing everyone but Sherlock when it becomes clear that the present is for him. Isn’t he a thoughtless snob? Not at all, says Cumberbatch; he simply has no time to waste. “That doesn’t make him a bad man. There’s so much in the 21st century that is stymied by bureaucracy and mediocrity and committee. It’s a great thrill to see someone cutting through that.”

Well then, is he, as his flat-mate and collaborator John Watson (Martin Freeman) suggests in a moment of frustration, “a machine,” who exhibits no emotional response when a dear friend appears to be in mortal danger? No, Cumberbatch sees his character as a loving, caring human: “You can’t be a master interpreter of behavioral science and the logic of human interaction in the way that he is—diagnosing people’s behavior, the evidence on their person, their psychology—unless you have an understanding of it.”

OK, but surely Sherlock is an attention whore—a celebrity who courts the tabloid press and enjoys the flash of the paparazzi. When Sherlock’s showboating performance in a high-profile trial turns him into even more of a public figure, he seems excited to find himself chased by packs of reporters. Still, Cumberbatch doesn’t think he craves the attention: “He doesn’t want fans. He complains to John about his burgeoning Internet fame, but he makes no bones about it when he’s being brilliant. He can’t filter that. He gets too much enjoyment out of it. It erupts.”

You might even ask if Sherlock deserves to be at the center of the show. In their loose interpretation of Doyle’s stories, Moffat and co-creator Mark Gatiss have beefed up the role of Holmes’ nemesis, Jim Moriarty, played with slimy gusto by Andrew Scott. Here in the antihero-loving United States—home of The Sopranos, Breaking Bad, Dexter, and Boardwalk Empire—this would surely have guaranteed Moriarty the title role in the series, but Moffat dismisses my dreams of Moriarty!, saying Sherlock’s much more interesting to him. He loves Sherlock’s striving for perfection; quoting with relish Conan Doyle’s description of Holmes as a man who “makes a special effort to be better than his human frailties might seem to allow him.”

Eliminate every alternative and what remains, no matter how unlikely, is the solution. So, what is the key to Sherlock Holmes? For Moffat it’s something usually missing from the world of TV: satisfaction. Sherlock Holmes is perfectly comfortable in his own skin. “As much as it may horrify us, Sherlock’s quite a happy man. He gets a bit bored between cases, but he enjoys himself. He’s got his best pal, he’s got his nice flat, and he goes out and has tremendous adventures. He’s unrepentant about how he is, because he honestly can’t see a damned thing wrong with it.” And the secret of his appeal? “If you met a man like Sherlock Holmes, and he was that clever, and that dazzling, you’d be fascinated by him. He would be absolutely magnetic. The fact that he is carelessly rude to you wouldn’t concern you at all. Fascinatingly confident, rude people are great.”

I suspect this is an opinion held in very few places other than the heads of TV writers. A real-life Sherlock, forever touting his brilliance and running rampant over fragile emotions, would be intolerable. But this TV version has an Achilles’ heel. Every so often, in moments of extremis—as in the final episode of last season, when he was willing to risk everything to save John Watson’s life—he reveals that his bluster and coldness is all an act: He loves us “ordinaries.” That makes us love him back.