In the summer of 2015, Lifetime debuted “Unreal,” a show that landed like a lightning bolt; with its mix of forcefully stated points about the media ecosystem in which we live and luridly soapy twists, the series was an instant hit, sweeping up Emmy nominations and breathless speculation about where it’d go next.

Some three years later, “Unreal” wrapped up its run with a final season dropped onto Hulu without ever airing on Lifetime. The show lost popularity and its critical luster as it attempted big statements without ever thinking through what it was trying to say; it came to feel as though its manic toggling from one big event to the next was less a sign of rich creativity than of a lack of real insight.

Lifetime has not captured the public imagination in quite the same way again in the years since “Unreal” debuted. But it has a real shot with the new series “You,” a flawed but compelling new drama that brings to mind both the sparky sensation of “Unreal” and the ways in which it was not built to last. Produced by TV impresario Greg Berlanti, this series stars Penn Badgley as a figure who goes beyond antiheroism—he’s a murderous stalker whose obsession with a young woman he meets briefly turns into the governing force in both of their lives.

Joe (Badgley) is a New York City bookstore clerk who rings up Guinevere (Elizabeth Lail) and takes it upon himself to learn everything about her — easy to do when her name is on the credit card with which she pays for a Paula Fox novel, and also on her unlocked social media accounts. After following her over the course of an evening during which she, coincidentally enough, slips and falls on subway tracks, Joe is able to play rescuer; soon enough, having worked to isolate Guinevere from an on-again, off-again boyfriend and from her friends, Joe will have Guinevere all to himself.

That’s the plan, anyway, one we hear about in voice-over as Joe’s fevered thoughts unfurl. The storyline here — much as it was in the source material, Caroline Kepnes’s novel of the same title — derives much of its charge from the ways in which Guinevere departs from the idealized woman Joe imagined based on nothing more than her name and her interest in buying challenging literature. Joe is masterful at cajoling Guinevere and telling her what she would seem to want to hear, and he makes great headway in taking over her life, but Guinevere comes with an unexpected core of independence, as well as secrets of her own. A clever irony of the show — and one of the sharper ways it addresses our time — is that even as Joe disdains Guinevere for her use of social media, he’s become addicted to the sunny and fun face she presents to the world. The more he learns that she’s as obstinately unlikable at moments, as inflexible and as wracked with darkness as he is, or at least close to it, the more frustrated he grows. He comes to act out in increasingly gory ways, trying both to win her loyalty and exorcise some inner darkness.

All of which could add up to a sharp social satire in the vein of “Gone Girl”; on this TV series as in that film, we’re barely meant to take every detail seriously. (To wit: Joe’s work behind the counter of a bookstore gives him access to a vault, meant for storing volumes, that doubles as a torture dungeon.) Unfortunately, though, Badgley at times stretches credulity; his performance, affably sardonic in much the same vein as his brooding Brooklynite from “Gossip Girl,” doesn’t add up to an individual capable of stalking and, eventually, murder. In voice-over, Joe speaks rapidly as he unspools his plans, but though his words are troubling, his tone is oddly free of mania or passion. Badgley’s Joe seems at times to have so effectively subverted whatever part of his personality is unmoored from morality that he forgets to show it to us at all. The show, depicting scenes of cruelty that exist less viscerally on the page, seems almost to shy away, showing us Joe’s monstrousness but compensating extra-hard by making him charming beyond belief. His facade almost never cracks, even in private.

It’s early going yet, and we may see more sides to Joe as the walls close in. But, for now, his insouciant charm even in his internal monologue is one fantastical element too many. The show asks us to swallow much that doesn’t track — that, for instance, Joe is a master sleuth who’s able to follow people silently without being observed and slip into apartments with ease. The audience will follow as long as it’s fun, but Joe’s character, with a Mr. Hyde hidden somewhere inaccessible within a lighthearted and charming Dr. Jekyll, grows frustrating.

That’s what leads to the question of how long “You” can go on for — even as, before it’s premiered, it’s been renewed for a second season. We see, very early in the show’s run, the heights of Joe’s depravity; he commits crimes that tend to make a character irredeemable in an audience’s eyes. And he does so without ever really convincing us that he ever could have. “You” has sharp ideas, if sometimes expressed with thudding lack of subtlety, about social media; it has an interesting premise; it gets the hip-young-literary-Manhattan setting as satisfyingly almost-right as did “Gossip Girl,” in the manner where its departures from reality end up feeling refreshing and fun. But it doesn’t quite have the courage of its convictions. In order to have a decent run, “You” will have to keep upping the ante, keep escalating a story that reaches an 11 in intensity in its first few installments. And it’ll have to push Badgley, an actor who already has our sympathies, but who hasn’t yet earned our fear.

Drama: Lifetime (10 episodes, five reviewed), Sun., Sept. 9.

Cast: Penn Badgley, Elizabeth Lail, Luca Padovan, Zach Cherry, and Shay Mitchell.

Executive Producers: Greg Berlanti, Sera Gamble, Sarah Schechter, Leslie Morgenstein, Gina Girolamo, and Marcos Siega.