ɫɫ��

But Sweeney’s provocative work — in which he stars as well as writes, directs and produces — swings much wider. From the very specific vantage point of twindom, he’s made a dark comedy — with a definite emphasis on the dark — that addresses the nature of grief. What was it Shakespeare said about love, that it looks with the mind, not the eyes? Sweeney’s film argues that grief is also subjective, and that it doesn’t always follow logical paths — or even acceptable ones.

His partner in this absorbing project is a terrific Dylan O’Brien, who earns double billing as two very different twins (he won a special acting prize at Sundance this year, where the film One is Rocky, a gay man who is outgoing, freewheeling, witty, self-assured. The other, Roman, is a straight man who is withdrawn, insecure, less than articulate and easily offended.

We begin with the sound of a crash, offscreen. And then a funeral. Roman is mourning his twin. Strangers come up to him, exclaiming how much he resembles the deceased. “I feel like I know you,” one says. “Oh God, your face!” Instantly, we realize this must happen to twins at funerals all the time.

The task of emptying out Rocky’s Portland, Oregon, apartment falls to Roman and his devastated mother (Lauren Graham, in a brief but searing performance), and Roman decides to stay on for a while. That’s when he happens on a twin bereavement group.

One of his fellow mourners is Dennis, who speaks freely of his own lost twin, Dean. Outwardly the two men would seem to share nothing. But Dennis reminds Roman of Rocky, and the two bond over shared experience and loss, eating together and buying groceries, even road-tripping to a hockey game. You almost expect a rom-com montage where they start shopping for clothes.

Dennis tells heartwarming stories about Dean, such as the time he subbed in for him on school photo day, and nobody was the wiser. The heartwarming goes to heartrending, though, when Dennis talks about the agony of loss.

He actually likes the pain, he says, “because if I don’t have the pain, then he’s really gone, and I’m actually alone.”

This would all be a great premise for a quirky bromance. But then, the opening credits run, fully 20 minutes in, just when we’ve forgotten to expect them. And here’s where things get complicated — for Roman and Dennis, but also for any effort to review this film. The major twists, which unfold as we rewind to where we started, are surely better left unrevealed.

Still, it should not surprise anyone that Dennis has deeper reasons for latching onto Roman, and as Sweeney’s plot unspools, we become more fascinated and horrified by the minute. Now we also meet Rocky, in flashback. In a few short scenes, we come to understand his easy appeal — and how different he is from his brother. While Rocky is quick-witted and clever, for example, Roman is slow to grasp sarcasm, and insulted by the slightest jab. O’Brien’s performance is a triumph of such detail.

There’s a third anchor here, a female character whose importance slowly grows: Marcie, the sweet-tempered receptionist at Dennis’ office (Aisling Franciosi, excellent.) Things all start crumbling when she invites Dennis to a Halloween party. Dennis brings Roman, and the two hit it off. (Sweeney makes ingenious use of a split screen to convey the differing experiences our characters have at this party.)

For a while, they essentially become a threesome. But the writing is on the wall: this is heading somewhere very messy.

That denouement is both violent — at one point, stunningly — and gentle. In the end, we’re left to ponder not only grief but loneliness, and the lengths people will go to fight it. Shakespeare had a line about that, too, referring to “the mystery of your loneliness.” In Sweeney’s disturbing but also oddly satisfying tale, that essential human condition retains its mystery.

“Twinless,” a Lionsgate and Roadside Attractions release, has been rated R by the Motion Picture Association “for sexual content/nudity and language.” Running time: 100 minutes. Three stars out of four.