Eating your cake while having it too appears to be the fundamental objective of Sam Taylor-Johnson’s adaptation of the first part of E.L. James’ bestselling BDSM trilogy. “Fifty Shades of Grey” advertises itself as edgy and titillating, but proves fatally tepid and boring, not just because it opts for reticent gentility over lurid melodramatics but also because it turns what might have been a challenging descent into the murky waters of sexual experimentation into a sappy tale of a strong girl’s redemptive effect on a S&M-addicted billionaire. In the end, the drabness suggested by the color in the title seems all too appropriate.

The plot, of course, is extremely simple. Anastasia Steele (Dakota Johnson), a mousey English Lit major approaching graduation in a college in the Pacific Northwest, is recruited by her ill roommate Kate (Eloise Mumford) to do an interview she has scheduled with Seattle entrepreneur Christian Grey (Jamie Dornan), a benefactor to their school and its upcoming commencement speaker. For some reason Grey is immediately taken by the girl, and after what appears a fairly straightforward, if slightly creepy, pursuit (visiting her at work, buying her some expensive first editions of her favorite author Thomas Hardy), eventually reveals his wish that she join him in a sadomasochistic sexual relationship of the sort he prefers, becoming a contracted “submissive” to his “dominant.” Smitten with him, she agrees after haggling over the details of the contract of consent he wants her to sign, but after a few initial encounters backs off, wanting instead a more “normal” romance.

There are a few other characters folded into the mix—most notably Christian’s adoptive mother Grace (Marcia Gay Harden) and brother Eliot (Luke Grimes) along with his security chief and general factotum Taylor (Max Martini), as well as Ana’s mother Claire (Jennifer Ehle) and friend Jose (Victor Rasuk)—but none of them are of any importance (or well played), and the story is for the most part a two-hander, so to speak—which might have been a strength if the characters of Christian and Anastasia were better fleshed out and acted. As it is, we’re given just a few hints about the difficulties in his childhood and upbringing that have shaped Christian’s psychological makeup (his biological mother was a junkie, and a friend of Grace’s recruited him as her submissive when he was a teen) and even fewer about what has made Ana who she is (mostly revelations about her oft-married mother, who’s so devoted to her current husband that she even skips her daughter’s graduation to tend to his needs). But the two remain sketches rather than fully rounded human characters, and the banalities in which they converse make them feel even less real.

They’re certainly not transformed into recognizable people by the performances of Johnson and Dornan. Certainly both actors exhibit the necessary physical attractiveness, at least as far as one can tell from the curiously timid sex-and-bondage sequences that, as cautiously shot by Seamus McGarvey and edited by Debra Neil-Fisher, Anne V. Coates and Lisa Gunning, resemble glossy magazine-style inserts rather than ecstatic encounters. Otherwise they make a curiously uninteresting pair, with Johnson overdoing the trembling lower lip while Dornan musters little beyond an icy stare and slight smirk, though he is quite a clothes horse, as an opening scene set in his elegant walk-in closet, somewhat reminiscent of “American Psycho,” demonstrates. (Christian’s pad is, in fact, an impressively sterile place, which proves that production designer David Wasco has done his job well, even if its elaborate Red Room—with all Grey’s instruments of perverse pleasure—is never put to much use.)

And ultimately that’s the essential problem with “Fifty Shades of Grey”—it’s a tease. Anybody going into it expecting anything really kinky to happen onscreen—which is what all the hype seems to portend—is going to be bitterly disappointed, because it almost immediately makes Anastasia the emotionally dominant part of the couple. We’re meant to take Christian as an imposing, domineering figure before whom the poor girl quakes and to whose lust she gives in; but even at their first meeting, though she’s klutzy, it’s Ana who’s really in charge, and before long she’s not only dictating the details of the contract to him, but endures very little of the treatment he metes out before calling a halt to the entire business and turning him into a lovesick swain even willing to go on a regular date, complete with dinner and a movie, if only she won’t dump him.

Theoretically that approach to the material could have worked had Taylor-Johnson chosen to go the Douglas Sirk route and treated the tale with some flamboyance. But instead what she offers is prim, decorous and careful in the extreme. There are isolated moments when a tongue-in-cheek attitude appears to good effect—that negotiation scene, for example. But for the most part it appears we’re meant to take the saga of Ana and Christian seriously, which is frankly impossible to do when it’s presented in such a flaccid, lethargic fashion.

The picture ends so abruptly, in what might be the cinematic equivalent of coitus interruptus if it were preceded by any excitement, that viewers are hardly likely to be left panting for more. As part of her preparation for their encounters, Christian provides Anastasia with “safe words” to use when the going gets too rough for her. It’s a measure of how unimaginative the narrative is that they’re “yellow” (for slow down) and “red” (for stop). But they’re still useful: though the movie’s plodding pace is unlikely to cause anyone in the audience to shout “Yellow!” while it’s unspooling, the plan to continue James’ trilogy on film might well lead one to scream “Red!” at the prospect.