If you're walking in Boston, you may wind up on the set

Lights! Camera! Firecrackers!

Cue the line of swirling dragon dancers and the plumes of smoke on the streets of Chinatown. The curious onlookers cover their ears. A giant crane affixed with big lights casts a dusky glow over the actors and extras as they rehearse their scenes for a movie that for now is being called " The Untitled Blackjack Project." The movie -- which stars Kevin Spacey, Laurence Fishburne, and Kate Bosworth -- is based on the true story of how a band of MIT students used card-counting techniques to win big in Vegas casinos.

For weeks, production crews have hop scotched all over Boston to shoot the movie. Message boards are abuzz with stories from movie-set vultures and student extras discussing the most recent shoot sites, what they saw, and how they might get in on the upcoming action -- if they can find out where it's happening.

Unlike the bigger productions with higher star wattage, such as "Mystic River" (directed by Clint Eastwood ) and "The Departed" (directed by Martin Scorsese ) , that filmed here in recent years, the blackjack flick has done its filming stealthily since the end of February, surprising residents and college students when staging crews pop up on their blocks. Many scenes have been shot in buildings, making it harder to find the sets. This past week alone, locals reported spotting crews at Boston University, outside MIT, inside an East Boston warehouse, and near Simmons College.

That's where Tascha Louise came face- to- face with Spacey.

"It was rather random but a cool experience nonetheless," says Louise, who was on her way to work as a teaching assistant when she stopped to smoke a cigarette and spotted Spacey across from her. "He was wearing a beanie and talking on a cellphone. He is the kind of person you see in movies, but you don't expect to see standing like 15 feet away. One of my friends was all flustered after seeing him."

The movie is based on the bestseller "Bringing Down the House: The Inside Story of Six MIT Students Who Took Vegas for Millions," written by Boston writer Ben Mezrich . Previously called "21," the movie does not yet have a title. Its director is Robert Luketic , whose films include "Legally Blonde" and "Monster-in-Law."

While the city has served as a giant set for the filmmakers, many people haven't noticed. The shooting schedule has been kept under the radar -- unlike when "Mystic River" filmed here and a publicist informed local media about daily shoots. With the blackjack movie here through April, good luck figuring out where they'll be next. Bloggers post plea s on message boards such as those on IMDB.com: "Where they are shooting this week/next week?" and "If anyone has any info, please let me know."

Kaitlyn Lloyd , 18, hadn't known about the local shoots until she walked right onto the Chinatown set Thursday night. "I thought it was like a festival," said Lloyd , a Northeastern student who was dining in the neighborhood with her friend Jennifer Spinelli. When they heard a crescendo of drumbeats pounding nearby, they followed the music and discovered the set.

"You can't really tell what's going on," Spinelli said as she watched the director order the crowd to move back 4 feet to make room for the drummers. Movie cameras sat wrapped in plastic to guard against the night's drizzle.

The crowds on this night added to the cinema-verite experience. It was hard to tell the extras from the accidental tourists. Local employees were also surprised to learn that a movie was filming in their midst.

Linda Mac , a manager at Hing Shing Pastry in Chinatown, said producers asked her to keep her lights on Thursday night and well into yesterday morning after she closed up shop at 6 p.m. Carina Wung , a hostess at the Rainbow Cafe down the street, was asked to do the same. She didn't have a clue what was going on until she saw production workers suddenly appear with equipment.

"With 'The Departed,' you see the big stars like Leonardo DiCaprio," she said. "We don't even know the name of this movie."

The dragon dance scene, which was filmed across from the Rainbow Cafe, involved Spacey and actor Jim Sturgess walking through Chinese New Year festivities. The crowds, holding sparklers, were incorporated into the background.

Among them was a trio of Emerson College film students who happened upon the shoot by chance after dining on Beach Street. The friends had a front- row seat to the dragon dancers.

"We live up the street, and we didn't know about this," said Noelle Meixell , 20. "They've been doing a good job [of keeping it a secret]."

Mikyung Kim , an Emerson film major, considered the experience educational. "This is what we are studying," she said. "This is what we are going to be doing one day."

As a soft rain fell over Chinatown about 9 p.m., people began to wonder where Spacey had gone. Was that him just ahead, near a crewman? Ah, no. Just another gawker.

Johnny Diaz can be reached at jodiaz@globe.com.