"When customers come, I know what they want," Bauong Bui says, sticking her head out of the cart to look down an empty 38th Street. It's 3 p.m. on a Monday, a bit past peak lunch hours. "Their names I forget right away. But the food -- what they want -- I know."

Bui is petite -- maybe 5'2" -- with short black hair in a ponytail and few wrinkles. She wears a blue half-zip Adidas sweatshirt and sandblasted jeans tucked into black sheepskin boots. A Penn girl's outfit.

Bui is not a Penn girl. She has owned Bui's Lunch Truck for 18 years, opened up restaurants in New Jersey and Maryland and built two beach resorts with her husband in Vietnam -- the country from which she escaped 30 years ago.

As she waits for the next customer today, smoke billows from the top of the truck into the grey sky. The generator hums. Sandwich scraps slip and slide down the oiled grill into the adjacent grease catcher, wafting the scent of burnt ham, egg and cheese down 38th. I stand there and exhale. My breath floats away into the cold with the truck's smoke.

Finally, a guy of average height and dirty-blonde hair approaches.

"So, do you know what he wants?" I ask.

"Sometimes, he wants plain steak," Bui says. "Extra ketchup. He never wants cheese."

"He never wants cheese?" I repeat.

"Sometimes bacon and egg. Never cheese."

I turn to the student. He nods yes.

I turn to Bui. She chuckles.

"You're good," I say.

Back in her native Vietnam, Bui was once considered an enemy of the state.

On July 2, 1976, Communist North Vietnam reunified the country under its Socialist Republic, ending a civil war that had displaced 6.5 million South Vietnamese and killed a million others. The new government's first course of action was to punish citizens who had affiliated with the South.

The government sent these Vietnamese to "re-education centers" and "new economic zones" -- labor camps and gulags. It confiscated Southern land and named enemies of the state, who'd be killed by firing squad if captured. Because her family worked for the old government in the South, Bauong Bui was considered an enemy. As was future Steak Queen owner Hoang Thuat -- though at age three, he was too young to know it. Thuat's father had served in the South Vietnamese Air Force, which sent him to the United States for training during the war.

When the war ended, Thuat's father was still in the U.S., and with the North having won, he could not return to Vietnam. So Thuat grew up without a father and went into hiding. He never attended high school. But Bui was luckier, if only by a little. She managed to escape Vietnam by boat, as two million others eventually did. Her family, however, stayed. The government locked up four relatives, including her father for eight years and her brother-in-law for 15.

Monday's grey sky turns charcoal and the cold seeps into customers' skin, cracking hands into crocodile flesh.

"Do you guys have a heater in there?" I ask Bauong Bui, eyeing the truck's interior, wondering if I can enter for a minute.

"We have a big heater," she answers, looking down at me from inside, where 45,000 British Thermal Units of propane-generated warmth cocoon her every hour.

Bui looks at me and grins.

I look north up 38th, wondering if other food trucks will take me in. Somehow, as the street grows darker, the trucks seem shabbier. I can now make out bird droppings, fender dents and rusted wheel arches. Bui says she likes this atmosphere, though, this street filled with food trucks. There's the Muchos Tacos cart, where she eats a Mexican lunch every now and then ("I don't know what it is, but they know what I want"). And KoJa, the truck with the two friendly Koreans on the corner of 38th and Walnut.

Only two carts over is the Steak Queen and Hoang Thuat. Once separated from his father at the age of three, Thuat now works to support his own three-year-old. He reunited with his family here 12 years ago, when he finally emigrated from Vietnam. Since then, he's worked in the food business, first as a dishwasher in Center City, then as a cook at a Cuban restaurant and now as proprietor of the Steak Queen truck (with his wife), on the same street as another former enemy of the state.

"It's always hard when you come here to get a new life," said Thuat's uncle, Vuong Lee, who sometimes lends a hand. "You have to learn the new language. When he decided to buy a lunch truck, I told him, 'This is an opportunity to make a living.'"

Thirty-eighth Street has always been a good place for food vendors to make a living. Situated between Huntsman and Superblock, 38th is the only street to cross the middle of Penn's campus. And unlike other food trucks on campus, those on 38th must sign a city lease for parking space, instead of one from the University. The city lease costs about $2,800 per year, but it allows 38th Street trucks to avoid Penn's often arbitrary rules, which once forced trucks to close by 6 p.m. and included a parking fee that rose from $1 per year to $400 per month in 2003.

At the very least, then, the food trucks on 38th are bonded by city law. But there's more to it than that, for Anthony Spadaro. A 33-year-old Drexel engineering grad, he opened his Muchos Tacos cart over a year ago in Northern Liberties. He figured he knew the food business, having served as manager of his stepfather's chain of El Azteca Mexican restaurants. He moved his truck to 38th Street last semester.

"I was shocked," he said. "I assumed there would be a lot of petty bickering -- that trucks would be saying to each other, 'You're an inch too close to me,' or 'You're stealing my customers.' But everyone has been really nice and outgoing."

So nice, in fact, that Spadaro and his fiancee will spend two weeks this May in Ho Chi Minh City, vacationing with the Buis at the Oriental Pearl, a resort the Buis founded upon first returning to Vietnam in the last decade. (Vietnam began reforming its economy in 1987, evicting many of Ho Chi Minh's remaining followers from government and enabling exiles to return.)

Spadaro said he plans to sell his cart to a former Starbucks manager so that he and his fiancee can move back to her native Sweden, where they hope to open a Mexican restaurant. "It should be sort of a novelty -- Mexican food in Sweden," he added. "But what's really bizarre is that when I attended Drexel and bought stuff from trucks, I felt bad for these guys, but it's not bad at all. These guys constantly help each other."

As the elder statesman of 38th Street, Bui is there to help. The Yue Kee Chinese truck has been around longer, since 1983, but its owners don't speak English and tend to keep to themselves. So if a truck runs out of supplies, Bui's is the one to lend it what it needs -- rolls, condiments, onions -- as long as the truck repays the food the next day.

"If a delivery is late, or I missed a delivery of hoagies, I'll just go and borrow," said Andy Mazaj, 20, owner of Donika's, which sells American wraps and sandwiches at 38th and Spruce. "That's just how it is."

Do you have kids?" I ask Bui, still waiting by her cart on 38th, waiting for the sniffling customers who will come with orders she already knows. It's dark on Monday, and Bui's Lunch Truck seems like a Hot Wheels car compared to Huntsman's glowing spiral. Like a small Lego plaything in a world of big-boy buildings.

Inside the toy, a yellow blob of egg batter sizzles, bubbles and bursts on the grill.

"I have one," she says.

"How old?" I ask.

"What do you think?" she asks me back. I'm about to laugh with Bui at her joke when she cranes her neck out of the cart. She stares me down, as if really asking: How old do you think I am?

"I have no idea," I say. "I really can't win here."

Bui breaks into a grin.

"She's 23. Graduated from NYU last summer."

"Does she want to get into the food business?"

"Later on," Bui says, pointing to her sister, who is working the grill behind her, "I think her son-in-law and daughter will take over this job,"

"So it will stay in the family?" I ask.

"The name will stay on the truck," she says, chuckling. "Bui's forever."

The food trucks of 38th Street share a little secret. Phil Sandick is an assistant director of the Kelly Writers House, and he found out by accident.

It was a sunny afternoon in early November, and Sandick waited on line at Muchos Tacos while the woman in front of him ordered half the items on the menu. When she left, he asked owner Anthony Spadaro why someone would order so much.

"That's the Steak Queen," Sandick recalls Spadaro saying. "She's been over here ordering all my food the last two days over and over again. She's trying to copy my recipes. It doesn't really matter. She'll never get my recipe, but she's gonna try to put it on her menu. She did the same thing to Bui's."

Spadaro would not confirm the story.

If they have stolen recipes, he said of Steak Queen, "they've done it incognito. They never made it obvious."

Andy Mazaj, the owner of Donika's, also refused to indict anyone.

"That goes on around here," he said. "I wouldn't find it surprising because it happened so many times. I know a lot of food trucks that have done that, but I'm not gonna name any names. But yeah, I know a lot -- especially on this street."

Steak Queen's owner didn't respond to the accusations because he still speaks little English, but his uncle said, "There's no such thing as copying.

"If you go to a restaurant and order a hamburger," Vuong Lee added, "it's a hamburger. And maybe customers come back and say it's too salty or too spicy. So then you change it. You have to have certain items on the menu when people come to you. But I don't think there's any competition. The working environment is friendly."

Muchos Tacos owner Spadaro likened the block to a family. And lest you think this a feel-good family, Spadaro would let you know they have their differences, too. He's moving to Sweden partly "to get away from the Bush regime," whose war in Iraq you can bet he doesn't support. Meanwhile, down the block, KoJa worker John Chung supported the war since its start, praying -- with hands clasped, in the back of the truck -- that his 24-year-old son in the Special Forces would come home from Kirkuk alive. He returned six months ago.

"I'm so happy he's back in the country," Chung says, adding that his son, a Temple graduate, knew a fellow soldier who was killed in action. He looks at his partner, Jae Sime, who nods. "Of course, we worried about him."

So the vendors are close, but Steak Queen has also been accused of taking that too far.

"He told some of the customers we're the same family," the Bui sisters told me. "We're not a family. Just from the same country."

All the same, the sisters understand where Steak Queen owner Hoang Thuat comes from. He's the new guy on the block, they said, and he's trying to establish himself in a country he doesn't know. A boy whose father left at three, he's trying to bank on the other 38th Street Vietnamese. Bauong Bui says they're all still friends.

Bui says a lot of things. But all of them emanate from up on high, from that truck she stands in above you, looking down. It's raining hard this Wednesday on 38th, so when I arrive at the truck, I decide to finally ask.

"Can I come in?"

Bui mutters in Vietnamese to her sister, who's working the grill. Then she turns around.

"Okay, when we have customer, you can stand in here," she says. "Just one and then you leave, okay?"

The truck seems bigger from the inside. The floor is covered with a plastic mat made to resemble wooden tiles. In the back left, there's that sizzling grill, slathered in egg and steak and cheese. In the front left, Bauong Bui stands over a metal counter that opens to reveal a horizontal refrigerator. To my right is the cutting board and condiment area. After one Bui grills the sandwich, the other cuts it almost in half (they always leave it slightly together), then douses it in ketchup, hot sauce, salt or pepper and wraps it in silver foil.

Through the side of the truck, Bui notices a heavyset an in his 40s walk down the sidewalk. Here's the one customer.

"This guy -- I know what he wants," she says, pointing. The guy now stands at the window, and Bui announces the order.

"Double egg-white with cheese," she says. "Ketchup, salt and pepper"