When it comes to this movie, count them in

Author and subject take part in '21'

A local screening of "21" drew (from left) producer Dana Brunetti, author Ben Mezrich, star Jim Sturgess, and MIT alum Jeff Ma. (Bill brett for the boston globe)

There's nothing particularly remarkable about Crossroads, a dimly lit Irish pub in the Back Bay brightened only slightly by a smattering of neon beer signs. Its very inconspicuousness made it a key setting for planning astonishing schemes, like how to win millions of dollars through a very calculated system of counting cards at blackjack tables.

"Crossroads is where it all comes together. This is a very special place in the blackjack world," said Jeff Ma as he perused a listing of weekly specials. He smirked when he saw that Wednesday is still free-pizza-with-a-pitcher-purchase night, just like it was when he was an MIT student in the early 1990s living in one of the nearby fraternity houses.

It was a recent Monday and the blackjack whiz, who cofounded and now runs a fantasy-sports website, was perched at a high table in the bar. He was in town from San Francisco, where he now lives, for a screening of "21," which opens March 28. The movie is inspired by "Bringing Down the House: The Inside Story of Six MIT Students Who Took Vegas for Millions," a dramatized retelling of the adventures of Ma and his over-achieving pals on what came to be known as the MIT Blackjack Team.

Next to Ma was Ben Mezrich, the Boston author of the book, which was published in 2002 and spent 55 weeks on the New York Times bestseller list. Ten years after first meeting, the two are not only great friends, they're each other's reason for the fame they're both enjoying.

"We're like parasites - we feed off each other," Ma quipped.

"Who's the host?" Mezrich cuts in, with comic timing that could turn Steve Martin's head.

Almost everything about how the movie came to be seems the stuff of fiction. First the MIT brainiacs won unfathomable sums of money in the early 1990s employing a sophisticated card-counting system that measures players' odds against the house, often working under the suspicious watch of casino bosses.

Enter Mezrich, a Harvard grad and fiction writer who'd penned a few pulpy thrillers. He was introduced to Ma at a party, recognized the narrative potential of Ma's high-stakes escapades, changed names and details, and scored a book deal. Kevin Spacey happened upon an article about the team Mezrich published in Wired just before the book came out and got in touch with the author.

Next thing you know his production company bought the rights, and a movie was shot last year in Boston and Las Vegas, with a cast including Spacey, Laurence Fishburne, and Kate Bosworth. Jim Sturgess, a young British actor best known for a starring role in the Beatles movie "Across the Universe," plays the character inspired by Ma.

For Ma and Mezrich, the ribbing is constant. Ma is fast with the wisecracks, while Mezrich, who describes himself as a younger Larry David because of their shared neuroticism, is more of the straight man.

"Other than Jeff, nobody wanted to be a part of this when I sat down to write it," Mezrich said. "Now everybody wants to be a part of it."

He was, after all, making a thriller based on playing cards before it was common to find poker tournaments on television. While card counting isn't illegal, counters can be banned from casinos. "It was a really secretive thing, and nobody on the MIT team had really talked to anybody," Mezrich said. "I was the first person to sit down to actually write this story."

"I open up to Ben often," Ma interjected, poker-faced.

The resulting book, and movie, is told through Ma's eyes, according to Mezrich. "The other characters were much less important and to some extent I changed their names, changed everything about them, and made some composite characters," he said.

He makes no claims that his volume is a scrupulously chronicled account. Rather, Mezrich said he is more interested in the mythic aspect of kids taking on and beating the system, a central theme of his other works. Even Ma's character is given another name - Kevin Lewis in the book, Ben Campbell in the movie.

The movie follows Ma's fictionalized counterpart from his recruitment by the clandestine club to becoming a "Big Player." That's the high roller who takes cues from teammates and only sits down at a table when the deck would be statistically in his favor. But being a BP requires more than mathematical acumen.

"A couple of things I think made me good," Ma said. "One was the ability to do so many things and keep the count. And the other is the ability to act and be gregarious and talk to casino people and not make them focused on the fact that I might be counting cards, but make them focused on the fact that I was the guy who's cool and effervescent and ebullient and all that."

When Spacey contacted Mezrich about turning his book into a Hollywood movie, the writer assumed it would then be out of his hands. But Mezrich said he was pleasantly surprised that he and Ma were aggressively brought into the moviemaking process.

"You're pretty much told a million times that authors don't get to be part of the movie, that you'll be invited to the premiere and that's about it," he explained. "But because I had a deal with Kevin early on and Kevin and I sold it together, basically I was in a position where I got to be on set, got to look at the scripts, got to be a part of everything every step of the way. Jeff got to be on set and consult as well."

While they didn't vet changes to the script, their main charge was to offer comments to make it all look "more real," said Mezrich. Apparently their input struck a chord with those who know the ins and outs of the system.

"The movie totally captures a lot of the excitement in a realistic way," said Bill Kaplan, a Harvard alum who in the early 1980s deferred Harvard Business School while he cofounded and trained the MIT team. (Kaplan believes the character Spacey plays in the movie is based on him; Mezrich said that he never interviewed Kaplan, though he believes others may have referred to him in stories that made their way into the book.)

With card-counting about to be glamorized in multiplexes across America, is anyone concerned that hacking Vegas will become a recreational pastime?

Unlikely, said Ma, who believes the book and movie make the endeavor seem a lot more fun than it actually was.

Only with drilling and training does the practice become instinct - and even then, only in the long run do winnings make up for the losses, Ma maintained. Plus, counters get recognized and casinos can ban them.

Ma knows this firsthand. To this day, he is widely recognized in Vegas and not allowed within 20 feet of blackjack tables.

Mezrich can't count cards. So it looks like they'll have to keep counting on their luck in Hollywood instead.