With documentary features continuing to gain ground as mainstream entertainment — lots of people are showing up for “Won’t You Be My Neighbor?” and “RBG” — their subject matters are becoming more intriguing and, in many cases, more peculiar. “Three Identical Strangers,” a darling at this year’s Sundance and Hot Docs International Documentary Festivals, clicks on both counts.

The opening sights and sounds are of 56-year-old Bobby Shafran, sitting down, looking into the camera, and saying, “When I tell people my story, they don’t believe it ... but it’s true, every word of it.” Then he calmly launches into that story, explaining that it really began when he was 19 and a freshman at Sullivan County Community College, where other students joyfully greeted him, many of them saying, “Welcome back, Eddy!”

“What? But I’ve never been here before,” remembers Bobby. And, by the way, “My name is Bobby. Who’s Eddy?”

Even after so much time has gone by, Bobby is still incredulous about the events that followed. The film shows some of them in a series of imaginatively presented old-style “flashbacks” that are actually color-saturated recreations of what went down.

But speaking as a movie fan and audience member rather than a critic this time, I’m only going to reveal a small amount of what happens in this film. The main reason is that I was so caught off guard right at the start and then again by the journey I was taken on as I sat there, open-mouthed and, on a couple of occasions, yelling at the screen, “No way!” or, using Bobby’s word, “What?”

My hopes are that your experience of watching this will be at least close to mine. I knew nothing about it, and I’m going to share only a little more here.

Those college kids weren’t completely wrong; they did know Bobby Shafran. But his name was Eddy Galland, who had been at the school the year before. Bobby Shafran and Eddy Galland were identical twins, who were separated when they were 6-months-old, put up for adoption, and raised by different families, never knowing that they were twins. Their eventual meeting was a game changer for both of them, resulting in the happiest of celebrations, along with local newspapers glomming onto their story.

One of the film’s many talking heads, a journalist named Howard Schneider, says that after writing about them, “the story went from amazing to incredible.”

That’s because 19-year-old David Kellman, who was also adopted, read the article, realized that he looked a whole lot like Eddy and Bobby, and noted that they all shared the birthday of July 12, 1961.

Yup, we’re talking triplets here, as is hinted in the film’s title. And if you thought there was some merriment when Bobby and Eddy found each other, imagine what happened when David got together with them. There are photos of them hanging out and partying due to their inevitable newfound fame. There are clips of them goofing around on the TV talk show circuit. Now there’s a wonderful and winning documentary for you.

But, giving away only that the film takes a strange turn, both in its story and in its mood, what you see at the beginning does not prepare you for where it goes. Among the other talking heads doing current interviews are some of the stepparents of the three guys, as well as each of their wives. It’s through them (and a few others) that dark secrets emerge, some of them involving the adoption agency, others coming from an organization called The Child Development Center.

OK, that’s enough. Disclosing any more would take away from the film’s effect. If your interest in piqued, and if that interest is attracted to studies of human nature, just go. There aren’t many documentaries that take you on such an intense roller coaster ride. This one’s an E ticket attraction.

— Ed Symkus writes about movies for More Content Now. He can be reached at esymkus@rcn.com.

“Three Identical Strangers”
Directed by Tim Wardle
With Eddy Galland, David Kellman, Robert Shafran
Rated PG-13