XX/XY opens with just the kind of primal sexual scene its title suggests. On a New York subway, a man (Mark Ruffalo) and a woman (Maya Stange) spot each other, as the film freeze-frames over telling, split-second glances of mutual interest. Later, when they meet unexpectedly at a party, a more direct flirtation seems destined to take them to the bedroom. Then the environment, a drunken party at Sarah Lawrence College in 1993, takes over where biology leaves off. Casting dating tradition aside, Stange suggests that her friend Kathleen Robertson be a part of what follows, but the unsatisfactory outcome of the proceedings reveals that Stange is motivated more by playfulness and the permissiveness around her than by deep-seated desire. While the trio never quite produces the dizzying peaks it might have anticipated, what follows is less predictable still. Stange and Ruffalo pair up, but they keep Robertson circling around, almost as if their thwarted threesome has been redirected into the kind of drawn-out drama of friendship and passion that only really makes sense until the world's demands kick in. First-time writer-director Austin Chick even uses the kind of falling-in-love montage usually reserved for giddy couples, but elsewhere, he keeps the direction low-key, providing just enough dialogue to get the job done, and letting the situation's joy and hurt speak for themselves. The hurt quickly overwhelms the joy, and later casts a shadow over XX/XY's talkier second half, which takes place in the present day, when all three players unexpectedly reunite. The 10-year bracket has convention going for it, but the film suggests other motives. Wearing a Dennis Miller smirk and facial hair that might have been grown simply out of whimsy, and unable to answer a question without sarcasm or misdirection, Ruffalo's character may be the first unflattering look back at Generation X; his inability to decide what he wants takes its toll on those around him, then on himself. Though initially off-putting, Chick's distanced direction pays off as XX/XY goes along. The first act's Bret Easton Ellis-lite indulgences give way to a second act in which words take the place of actions, but do little to dull the ache of unrequited desire, lost opportunities, and thoughtless indulgence. XX/XY features a grim moralism that its flashes of humor only underscore, but the cast and characters invest Chick's tug of truth and consequences with the authenticity of an accidentally observed moment. Chick opens on a world with no strings attached, then pulls back to show that the strings stretch to infinity.