This undated photo provided by film studio Neon shows Eddy Galland, from left, David Kellman and Bobby Shafran, three brothers who learned at age 19 that they had been separated at birth.

“THREE IDENTICAL STRANGERS” — 4 stars — Robert Shafran, Eddy Galland, David Kellman; PG-13 (periodic profanity and some frightening adult themes); in general release

The story feels almost too absurd to type: In the fall of 1980, Bobby Shafran walks onto the campus of a New York community college for the first time at age 19, yet everyone there already seems to know him. In fact, they know a different student named Eddy Galland, who turns out to be Bobby’s long-lost twin brother. Each was adopted and neither knew the other one existed.

Bobby and Eddy hit it off, and a newspaper circulates their amazing story. David Kellman reads the story and is dumbfounded: Bobby and Eddy look just like him. The long-lost twins are actually triplets. All three unite, become celebrities and open a restaurant in New York City.

This sequence of events sounds like the setup for a wacky 1980s comedy, yet it is a true story and the subject of Tim Wardle’s documentary “Three Identical Strangers,” which ran earlier this year at the Sundance Film Festival.

Here’s the thing, though. That opening summary at the beginning of this review? That’s just the first 10 minutes or so of the film. Their reunion is so engaging and it happens so fast that before you reach the end of the first act you’re left wondering: How is Wardle going to fill the next hour? The amazing story has already been told.

That’s when, as a family friend suggests, “things kinda got funky.”

A lot of perfectly good documentaries show their cards early, establish a unique premise and let the audience explore a topic at a leisurely pace, without much in terms of surprise. “Three Identical Strangers” is not one of those documentaries. It’s feel-good opening is just the beginning of a fascinating dogfight of a narrative that keeps dropping bombshells up until the closing credits.

This undated photo provided by film studio Neon shows Eddy Galland, from left, David Kellman and Bobby Shafran, three brothers who learned at age 19 that they had been separated at birth.

As the second act opens with Bobby, Eddy and David living the high life in New York, we're told their adopted parents are growing suspicious of the amazing turn of events. As young children, each of the boys received regular visits from representatives of the adoption agency that placed them, conducting tests and interviews under the notion that they wanted to study the outcomes of the adoptees. But there was much more to the story, and it turns “Three Identical Strangers” on its head.

To say more would give too much away, but as Wardle’s film winds its way through a staggering narrative, it explores a dynamic range of themes — from the importance of family to the ethics of scientific study to the long-debated question of whether our nature or our nurturing has more to do with who we become. It’s a stunning journey, and even if the rest of the story doesn’t quite maintain the happy vibe of its enthusiastic opening, it is well worth taking.

Plenty of good documentaries can live off the quality of their engaging subjects, but Wardle elevates his effort with masterful storytelling. The means are routine: Talking head interviews with the brothers, different friends and family members, and eventually, some of the people involved in the brothers’ childhood studies. It’s all intercut with old video clips and still photographs — nothing all that out of the ordinary. But the way the story unfolds, and the way new characters are introduced, makes “Three Identical Strangers” a truly compelling film.

“Three Identical Strangers” is rated PG-13 for periodic profanity and some frightening adult themes; running time: 96 minutes.