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Backed by Alison Moyet warbling in French, the pastel-hued animation of XX/XY’s opening credits prepares us for a romantic comedy. Within a few minutes, however, first-time writer-director Austin Chick plunges the audience into a relationship movie of the kind that can transform a relaxed date into a cranky late-night skirmish.

The first half of Chick’s underwritten but intermittently affecting screenplay takes place at Sarah Lawrence College in 1993. Party-animal classmates Sam (Maya Stange) and Thea (Kathleen Robertson) hook up with aspiring artist and filmmaker Coles (Mark Ruffalo) at a school bash. The three pile into bed, but Sam’s uneasiness terminates the anticipated erotic hijinks. Coles is drawn to vulnerable Sam, whom he continues to bed casually while enjoying flings with other women. Sam’s attempts to extract some sign of commitment from self-indulgent Coles fail, and after an especially vexing betrayal, she abandons him.

Chick’s narrative then leaps forward a decade. Following the failure of his fledgling effort as a movie director, Coles has lowered his sights and is working as an animator for an ad agency. For five years, he’s lived complacently with his loyal, sensible girlfriend, Claire (Petra Wright), in a trendily sterile white-on-white apartment. By chance, Coles bumps into Sam, who has just returned to Manhattan after breaking an engagement in London. They furtively resume their once tempestuous affair, which is exposed during a weekend in the Hamptons hosted by Thea and her restaurateur husband, Miles (David Thornton).

Although XX/XY’s title implies that Chick intends to draw some distinctions between the needs and drives of men and women, selfishness appears to be the basic motivator for most of his characters. But the contributions of the director’s talented cast do enliven his rather shallow and schematic vision. As in his breakthrough role as a drifter in 2000’s You Can Count on Me, the darkly magnetic Ruffalo demonstrates a rare gift for playing characters driven by complex forces they can’t fully comprehend. Other actors would be content to portray Coles as a womanizing skunk—which indeed he is—but Ruffalo, with his wormy smiles and haunted eyes, refuses to pass judgment on his character, endowing him with undertones of frustrated ambition and insecurity, and even adding a few grace notes of tenderness.

Blond, sharp-featured Wright turns in a thoughtful, muted performance as the least attractive but most sympathetic of Coles’ women. Her sensitivity to others—exemplified by the rare box set of videos by French filmmaker Claire Denis that she obtains for Coles—contrasts boldly with the self-centered behavior of her rivals. Physically and temperamentally, pert, round-faced Stange brings an appealingly Drew Barrymore-like quality to Sam. Although easily wounded, Sam harbors an inner core of strength that she manifests in the movie’s climax. Robertson’s Titian-haired Thea, by contrast, shifts so drastically from perverse punk wildcat in the college scenes to rock-solid entrepreneur and spouse in the contemporary sequences that it’s hard to accept the transition.

But the fault may not lie with the actress. In a press-kit interview, Chick obscurely explains that several of Robertson’s key sequences were dropped: “[F]or various reasons, several of Kathleen’s scenes didn’t make it into the final cut of the movie. They’re some of my favorite Thea scenes, and they provide further insight into her character. I’m hoping they will be on the DVD.”

The director does manage to touch a few raw nerves and create some nicely detailed sequences—a dinner party shot in closeup by a restless, swirling camera; two characters flossing during an edgy conversation. But he has little to say about gender differences apart from the old news that men are more likely than women to bolt from relationships. If XX/XY is worth seeing, it’s as a showcase for talented performers who are destined to snag more challenging roles in better movies.

Like XX/XY, Identity is split into two sections. The first and, unfortunately, the longest is yet another rehash of Agatha Christie’s And Then There Were None, thrice filmed as Ten Little Indians and often cribbed under other titles. Identity’s second—and far more provocative—act is enigmatically hinted at several times during the initial hour-and-a-quarter, but it doesn’t kick in until 20 minutes before the movie’s Carrie-cloned climax.

In Identity’s Christie-hand-me-down scenario, recycled by screenwriter Michael Cooney, 10 strangers seek shelter from a pounding thunderstorm in a shabby motel run by a neurotic night manager. These refugees include a peevish actress (Rebecca DeMornay) and her exasperated limo driver (John Cusack); a policeman (Ray Liotta) transporting a deranged killer (Jake Busey); newlyweds (Clea DuVall and William Lee Scott); a hooker determined to clean up her act (Amanda Peet); and a distressed middle-aged couple (John C. McGinley and Leila Kenzle) with their creepy mute son (Bret Loehr).

Director James Mangold sets the explicit (but not emetically graphic) murders in an atmosphere that couldn’t be much grimmer or noisier. The torrential storm never subsides, forcing the actors to bellow their lines over both the elemental tumult and Alan Silvestri’s clamorous musical score. (People subject to migraines should probably bypass Identity.) Character-packed thrillers like this often leave little room for performers to make much of an impact, but Peet has some minxish moments as the sweet-and-sour tart, and John Hawkes, as the flaky motel manager, revives memories of the immortal Norman Bates.

If you’ve seen one serial-killings-in-a-cloistered-spot movie, you pretty much know what to expect. At one point, Cooney’s screenplay halfheartedly flirts with the overworked conceit that the murders are the vengeful consequence of the motel’s usurpation of an ancient Indian burial ground. But overall, Identity offers little to refresh this worn-down genre—that is, until the perspective-shifting, psychologically derived twist that professional ethics forbid me to disclose.

This surprise whammy, though challenging and offbeat, subverts the rules governing the formulaic stuff that preceded it to such a degree that the viewer feels rudderless and slightly betrayed. The movie would have been a far richer and more satisfying experience if the screenplay’s cunningly concealed stratagem had been exposed early enough to articulate the script’s ostensible concerns. As it stands, Identity is peculiarly unbalanced: a routine, headachey horror movie capped by the germ of a potentially clever psychological thriller. CP