After the wardrobe inspection, the casting director hops onto the chair again and announces a raffle. Theater tickets! Gift certificates! A signed jersey from the Minnesota Vikings! This is starting to feel less like Hollywood and more like a church picnic. Maybe the filmmakers researched Minnesotans and discovered this is what we enjoy. They want to make us feel at home. But we don’t want home. We want Hollywood.

By hour three, the holding area looks like an airport gate several hours after the plane should have left. Extras of all ages and sizes are sprawled across the floor. The beehive woman rolls her chair toward me, rips open a bag of potato chips, and throws it on the floor with a force I find excessive and vaguely alarming. The extras have divided themselves into little groups: Retired Policemen, Teenage Kids Who Look Like Models, Trendy Moms in Denim Jackets. I’m hungry, woozy and certain I’m in the process of catching airborne diseases from breathing the exhalations of every person in this room. I scavenge the snack area, but all that’s left is an empty bag of pretzels and half a glass of Gatorade. I picture myself living and dying in the extras’ holding area, begging pretzel crumbs off a phalanx of coiffed women in fashionable outerwear.

I’m sitting in this windowless, hangarlike room, in downtown St. Paul, Minn., at 3 p.m. on a Tuesday afternoon, because for the last two years, I worked as a writer for the radio show “A Prairie Home Companion.” Garrison Keillor, who hosts the weekly mix of live music and sketch comedy, had been writing the show for almost three decades when, a few years ago, he decided to hire some writers to assist. My job was to create new scripts and edit, or “punch up,” scripts that others had written — namely, Garrison himself. I wrote jokes, inserted topical humor and created realistic dialogue for teenagers. I liked the work, and the miniadrenaline rush I felt in the precious few hours before each show, poring over scripts to come up with new jokes about juvenile delinquents or exploding dinosaur eggs. But after two years, I decided I wanted to try out life as a freelancer, for “Prairie Home” and elsewhere. The instant I left, Robert Altman and a fleet of Hollywood royalty descended on St. Paul to make a movie version of the radio show — our radio show — a special gift to me from the angel of bad timing.

It’s not as if I imagined Bob and I would bond over lutefisk sandwiches at Mickey’s Diner, trading stories about “the biz” as I offered him a sip of my malted milkshake. For one thing, our “bizzes” were different. He worked in glamorous locations all over the world; I worked in a squat brown office building in residential St. Paul. He directed some of the great actors of our time; I directed the cleanup at our annual Halloween potluck. Nonetheless, it seemed like cruel irony that just as I departed for greener pastures, a Technicolor one would drop into my backyard.

At the same time, I was skeptical. The movie, which opens June 9, was supposed to be a “behind-the-scenes look” at the radio show. But frankly, most of the behind-the-scenes work takes place in an office filled with copy machines, white boards and beige carpeting — not exactly a filmic vista. Backstage is a similarly non-photogenic mess of cables and old PCs. During the live shows, actors read from scripts while a sound-effects artist crunches Styrofoam plates, and Garrison tells stories while sitting on a small red stool. The show is built for the ear, not the eye — the whole world of the radio show is transmitted through sound effects, music and the human voice. It’s a world, but a world in sound, and it lives in the imagination of the listener. A film? I thought. Pshaw. Then one day, the phone rang: It was the “Prairie Home” staff, offering me a role as an extra in the movie.

I’ve never been a movie fanatic, but within hours of the phone call, I was printing out a blurry head shot to bring to the casting office. No big deal, I assured my family and friends. I’m doing this for my family and friends, I explained to the casting people. Neither was true. I accepted the role. This, as they say in the movies, is my story.

Most of the extras are out of work, retired, self-employed or on vacation. (A freelance writer, I fit into all these categories.) Near me, a group of moms are gathered in a semicircle around a high school student in a clingy coral top. They coo over her, peppering her with questions about her friends, her classes, her boyfriend. Across from them, a retired policeman spots an old acquaintance and updates him on the last five years of his life, which have included the death of his son. The policeman is accustomed to dealing with difficult situations; he’s witnessed the way people’s lives change in an instant. “You get those calls all the time,” he says, “but you never think it’s going to be your own son.” I strike up a conversation with a college student who wants to be a doctor. “I’ve already delivered a baby,” he says. “I was at a family picnic in a park. We heard screams, and I just rushed over. I’d seen babies born on TV, but still, it was unreal.”

All at once, a crackling instruction comes through the casting director’s headset, and a woman with dyed black hair climbs onto the folding chair and shouts, “Amber’s group! Amber’s group! Come to the stairs!” A whisper courses through the crowd. Twenty of us rise from our seats and crowd onto the landing. As we walk across the street to the theater where the filming is taking place, a mom sees Kevin Kline, one of the movie’s stars. “I just had a heart attack,” she whispers to her friend, “and I’m just going to keep on having them.”

We shuffle gingerly though the theater’s front doors, tiptoe past a woman painting a mural in the lobby, and file into the house. This velvet and gold theater has been my home turf for two years, but now it’s unrecognizable. A long platform extends into the middle of the house, and dozens of black-clad crew members scurry back and forth between the platform and the stage. Along one aisle, a pair of cameramen cruise up and down a track on what looks like a giant riding lawnmower. Black headsets perch on the seats like oversize tropical beetles, and a 20-foot arm with a camera on one end swoops back and forth across the width of the house. The Guys’ All-Star Shoe Band — the four musicians who appear every week on the radio show — are huddled in the middle of the stage like stunned tourists on Hollywood Island.

We’re barely seated when a voice booms: “Richie, are you ready to fight your way out of this one?” Richie, the pianist and bandleader for the Guys’ All-Star Shoe Band, cups his hands around his mouth and shouts back: “Yes, sir!” I turn around to see a fortress of monitors and consoles in the far back corner of the theater. Production assistants buzz around its perimeter, entering and exiting like worker bees bringing gifts of honey to the queen. Altman must be in there, I think, and for a moment I picture the Wizard of Oz, a tiny man behind an enormous letterbox screen. Just then, a sturdy-looking man with a rug of salt-and-pepper hair emerges from the fortress and walks out onto the platform in front of us. He turns out to be Vebe Borge, the assistant director. “You’re the audience,” Vebe instructs, “so we want you to clap. But try not to make any noise — we’ll dub over it later. And don’t stand up — the boom will knock you over.” We practice clapping without making noise, stopping our hands the split second before they hit each other.

Then there’s a shout of “Let’s go!” from the fortress, and Meryl Streep and Lily Tomlin strut onstage, their costumes draped lavishly over them, their hair glinting in 20 shades of gold and copper. The crowd gasps — there they are. No fanfare, no minions, just a couple of human-size people standing 10 feet in front of us. Their characters, Rhonda and Yolanda Johnson, are sisters, and singers in a family band. They laugh and twirl and poke at each other (“Where’d ya get that Kleenex? Down your front?”), all the while running through their lines. Their teeth gleam under the lights. I have never seen teeth so luminous. Meryl delivers a story about their dear mother, a poor washerwoman whose smile was as “wide as the Mississippi River…” She pauses for effect and then continues: “Down at the mouth.” Meryl seems like an embodiment of womanhood itself, and even her description of a river sends a frisson of erotic glee through the crowd.

And then they begin to sing.

Meryl belts out the first half of the song, Lily joins in, and now they’ve got their arms around each other and they’re swaying and grinning, their voices rich and mellow, the notes pouring out and washing over us. Forty eyes and ears are focused on one thing only. And all at once, we’re not extras playing an audience, we are the audience, and when Meryl croons, “Oh, the world is a world of rivers, flowing to the sea  And oh that mighty Mississippi  that’s where I want to be!” I’m thinking: Yes, Meryl! It is a world of rivers! They are flowing to the sea! Yes! Yes! And when they fling out their arms and belt the last bars, we leap to our feet, cheering wildly, whistling, clapping, waving our hands over our heads. We’re cheering for the performance, for the actors, for the fantasy, for ourselves. “OK,” says Vebe, walking out onto the stage. “But next time try not to make any noise.”

Later, I turn around to see a bunch of regular “Prairie Home” musicians in the back of the theater. Most of them have been recruited to play bit parts in the movie, and they’re all dressed in costume, sitting quietly with their instruments. Among them is Spider John Koerner, a regular guest on the radio show who is often cited as one of the most original performers in American folk music. He almost shouts his spare songs, and he speeds up and slows down to push and pull listeners through the music. Bonnie Raitt and Bob Dylan credit him as an influence; his playing style is so unique that even traditional songs sound like his own. Now he’s leaning forward in his seat, watching actors perform onstage. They’re stomping their feet and telling jokes, just like he does in real life. With costumes and scripts, they’re stepping into roles that mimic the life he actually lives. In the half-dark, I can’t quite make out the expression on his face — amusement, surprise, a flicker of weariness? I’ve been seduced by the performance — to me, it’s a glammed-up version of the creaky show I know so well. But I’m not the one being portrayed onstage. And I wonder if seeing strangers prance and joke like this makes him feel a little more vaporous in his skin, a little less solid. Spider John sees me watching him, and our eyes meet for a moment. Then, we both turn back to the stage and watch as our world is turned into fiction.

It’s day two, and we’re shooting the big finale — a couple of solos, a group singalong and a big bow. As I make my way past the cafeteria to the extras’ holding area, the beehive woman totters past me on heels, and the posse of moms scurries up the stairs. I’m about to follow them when I witness a scene like something out of Garrison’s fever dreams: Everyone who has ever been associated with the radio show, in its 30-year history, is eating lunch together in a giant cafeteria. Musical guests from the 1970s, current technical crew, radio actors and Garrison himself choose lunchmeats from a long buffet line. Sue Scott, an actor on the radio show who plays the makeup lady in the movie, is sitting next to Richie, the real-life bandleader. Richie is being followed around by the actual movie’s makeup lady, who is brandishing a foam wedge and powdering his bald head.

And then, into the middle of the cafeteria wander fictional characters from the radio show. Dusty and Lefty, the perpetually displaced cowboys from the sketch “The Lives of the Cowboys,” are walking around, life-size, in the form of John C. Reilly and Woody Harrelson. They amble through the lunch line in chaps and cowboy hats, looking as out of place as the characters in the sketch. Guy Noir, the bumbling private detective from the sketch “Guy Noir, Private Eye,” strides about in suspenders, in the form of Kevin Kline. He’s imperious, and he lifts his chin as he walks around the lunch tables.

Lunch ends, and all the extras shuffle into the theater to again play an audience, this time for what seems like all of Hollywood: Meryl and Lily, Woody and John, the diminutive Lindsay Lohan, Maya Rudolph from “Saturday Night Live.” Take after take, the mood onstage is upbeat — everyone’s whispering and laughing, or twittering around the piano. Lily Tomlin grabs a cowboy hat and plunks it on Lindsay Lohan’s head. John C. Reilly does rope tricks on the side of the stage. We cheer when he succeeds. We cheer when he fails. We love cheering, apparently, and he loves it, too. The cameras seem to be rolling or not rolling indiscriminately. Scripted laughter and genuine laughter blur into one another, and I can’t tell if we’re rehearsing, or shooting, or just goofing around. Are the actors acting like people having a good time, or are they actually having a good time? Are we? I have no idea.

The scene ends, and Meryl swoops across the stage, throws her arms around Garrison, and kisses him fully on the lips. The extras stare in disbelief. Was this for real? Was this ad-libbed? No one knows, and it doesn’t matter. “That’s good!” Altman shouts from the back of the theater. “And bring out the cowboy hat next time, too.”

Two weeks later, I go back to the set. There’s nothing for the extras to do, but I’ve heard they’ve built an entire office for Guy Noir, and I want to see it. The radio staff, I learn, has a sort of special status on the set; we’re walking relics, and the film crew looks at us with a sort of wary respect. “You work for the radio show?” they ask, squinting, like someone’s just pulled a set of vacuum tubes out of the storage closet. We’re living history, a precursor to this movie — and, as a radio show, to all movies. The film crew seems genuinely curious about us, the way you might be if Homo habilis knocked on your door.

Today the theater is empty except for a few strays like me and two flat-screen monitors hiked up on poles, with electrical tape marking the letterbox area. I slip into the wings, where the filming is taking place, and what I see before me is a shock. I’ve become accustomed to seeing fictional characters walking and talking, but now I’m standing in front of a meticulous physical rendering of Guy Noir’s office, the setting where each Guy Noir script begins. For the past two years, I’ve carried this office in my imagination. I’ve puzzled over the right sound effects — creaking drawers, ringing phones — and I’ve constructed scenes that occur inside it. Here, in front of me, is every physical detail, exactly as I’ve imagined it: crusty tape dispensers, Venetian blinds, a rusty fan blowing bits of paper. There’s an ancient metal mailbox, yellowing postcard pinups, and a few dusty fedoras hanging on the wall. A dim red light pokes from behind the blinds, like a stoplight shining from the street below. But rather than feeling like an intrusion into my world, it’s magical: This space is something I visualized completely, and here it is, in the flesh. Every inch of it fully described, fully realized. How strange, to wake up from a dream and find that it’s all been made real.

In live radio, the line between truth and fiction is impossible to ignore. The world of the radio show is obviously constructed: Headphones, microphones and scripts are all in plain sight. In fact, part of the thrill of watching live radio is seeing how the sounds that land in the ear as “true” are actually built. You can close your eyes and listen to a man walking through a rainy street or open them and watch the sound-effects artist splashing galoshes in a tray of water. You can listen to a married couple snuggling on the couch, or watch as two actors wearing headphones — and standing several feet away from each other — read from scripts. In radio, the performers and the audience are in on the joke together: The jig is up, as everyone can see. But movies are different: They rely on suspension of disbelief. Now, on this set, my disbelief is on the verge of disappearing entirely.

Then, Guy Noir enters the office, followed by Dusty and Lefty. And the fictional world of the radio show cranks to life. Guy Noir sits down, opens a desk drawer, and begins to roll a cigarette. Lefty strums a badly tuned guitar. Guy Noir chucks the cigarette and fiddles with his phone. Lefty begins to sing. I’m speechless; it’s as if the hours and years that have gone into writing, performing and listening to these characters — into, essentially, believing them — has finally made them real.

They’re ready to start filming. Kline blows his nose, and then leans forward for a nostril touch-up. The makeup lady scurries toward him and whips out a tiny sponge. The actors are about 5 feet away from me, and I haven’t cleared my spectatorship with anyone. I sidle up to a cluster of interns, hoping our matching black outfits will camouflage the fact that I have No Reason to Be There. An assistant to the assistant director walks over to where I’m standing. “Does everyone here know who everyone is?” he asks, looking directly at me.

The interns look at each other and shrug. I look down, suddenly fascinated by the pattern of bricks in the wall. One of the interns asks me if I’d like to have a folding chair closer to the set. She thinks I’m Someone. I’m not about to disabuse her of this notion. Oh, no, that’s OK, I say magnanimously, gesturing for someone else to take the chair.

The scene ends, and I walk into the lobby to scope out the snack options and run smack into the extras’ casting director. She looks surprised to see me. “Oh, hi,” I say, casually helping myself to a handful of dried fruit, “I’m just here to visit.” She smiles uncertainly. “Maybe it’s time to go,” I think, and steer myself out the door.

A Wednesday night the following week, I’m in downtown St. Paul for a freelance gig. It’s 11 p.m., and I’ve been working since early morning. Just for kicks, I walk past the theater to see if anything’s going on. The street outside is lit with powerful lamps, and the film crew is huddled near the theater’s doors. It’s the last night of filming. A large man with a fire hose is soaking the pavement to create the effect of rain. One of the interns recognizes me and shouts across the street, “Are you in this scene?” I haven’t eaten dinner, and I’m so exhausted I can barely stand up. The camera boom dips down toward me, then up. “Yes,” I shout back, “I’m in this scene.”

I head to the extras’ holding area to check in with the casting director. “You can be in the scene,” she says, glancing at my short sleeves, “but you’ll need a sweater.” I have no idea how I’m going to find a sweater at 11 p.m. in downtown St. Paul, but by some Hollywood magic, a woman who works in the box office wanders in and tells me she has a blue cardigan I can borrow. I follow her to the office, try on the sweater, and glance in the mirror. I’m about to be immortalized in a baggy, electric blue sweater with a large patch on the pocket in the shape of a globe. But there’s no time for vanity. I thank her profusely and dart back to the holding area.

All the regulars are here: the retired policeman, the trendy moms, the lady in the floppy hat with the self-love purse. Soon a big group of us is summoned down the steps and stationed across the street from the theater. It’s cold tonight, and the wet street makes it feel colder. We’re supposed to act like a crowd just arriving for the first time to watch the show. Some of us are instructed to smoke outside the theater, some are instructed to hang back near the fence. We attempt take after take; first we’re too clumped together, then we’re too fast. We’re having a hard time getting it right: We’re too enthusiastic, too quick to get to the front doors, not relaxed, the way a real crowd would be.

Finally, the assistant director is satisfied. He gestures to the cameramen and yells, “Go.” I leap off the curb and over a puddle, and hustle past the smokers and loiterers stationed outside. If you see the movie and the scene hasn’t been cut, I’m the one in the baggy blue sweater, ticket in my hand. The night is falsely bright, the street is falsely wet, and I’m dashing through the theater’s front doors like I’ve never been here before, like the night hasn’t even begun, like I’m about to see something wonderful.