We slide and rattle through the tunnel and the guy by the door starts mumbling. I glance at him. His pants cuffs are frayed and soiled. The soles of his shoes are thin. He carries an enormous dirty bag. He looks like an out-of-focus photo. He begins to mutter.

"'Puter 'puter 'puter," I think he says. He reaches into his pocket. I catch my breath and wonder where to dive as he pulls out the black butt of an Uzi. No wait. It's a flip phone. I breathe again.

He stares out the black window of the train as the bare yellow bulbs of the tunnel fly past. He puts the phone to his cheek. "Computer!" he shouts. The phone squeaks and beeps. My two-year-old Alex has a phone like that. His grandpa bought it for him in Chinatown for a dollar.

"Computer, make the train go faster!" the guy shouts.

I keep my eyes right on my book. I know with a subway rider's experience that no one is looking at this guy, that they'd stare into the sun rather than look at this man with the phone and frayed pants and the wild voice. New Yorkers just live with it, and read.

"Computer, make the train go faster! A hundred miles an hour! Computer!"

He must be a Star Trek fan. Amazingly, the lights of the tunnel start to zip by faster.

"Thank you, computer," he says, and seems satisfied until the train slows down coming into the next station. "Computer!" he shouts. I don't know why he's shouting. Who could know? I still don't know when I change cars at 72nd Street.

I feel like a tourist. This tactic almost always means giving up your seat, but I'm getting off soon, anyway.

At the next stop, I head up the stairs to catch my cross-town bus. The air on the street is cool and sweet; I breathe it as if I'd just been let out of a little box. The sidewalk seems to offer endless room to get out of people's way.

I catch the bus, and within a few minutes have crossed Central Park , a quiet ride: passengers murmuring into their cell phones, no cries of "Computer!" -- then I get off and start walking up Fifth Avenue.

This takes me gradually into a corner of Manhattan that used to be unlivable. One block east, housing projects are still stamped all the way to 125th Street. Fifth Avenue is No Man's Land, especially late at night: too nice for the bad guys and too bad for the good guys. I can manage it. I just don't walk east.

I walk north. Walking the avenues in New York is like driving fast down a long, wide highway: You should look at what's coming far ahead. I do, and I see a clot of kids in puffy jackets crossing to my side of the street. A lot of people are out and, more important, I can tell from two blocks away that none of the kids is taller than the roof of a car. If they were five years older, I'd keep an eye on them, my legs tingling as they got closer. But they're little kids. Little kids only do things to other little kids.

We near each other. They cross the street and strut and bob in my direction, their puffy jackets getting bigger, like grenades rolling toward me. When they reach my side of the street I'll be at least four or five steps beyond them.

Then from their little crowd, I hear snapping, like cap guns. They have those explosive little balls - you can buy those in Chinatown - that they slap onto the pavement. They creep closer. All four have something in their hands. Something dark and long that they hold tight. I keep walking. They chatter.

I look up, breaking their chatter. One of the boys looks at me and levels a black plastic pistol with a bright orange tip on the muzzle. The boy stares at me. He's about 12.

"Gonna shoot you motherf----r!" the boy says.

I keep walking. I wait for the snaps and snarls to get closer. They don't. The pavement feels solid under my feet. My stomach relaxes. I imagine what would have happened had I been half a dozen steps slower coming north on this street. Right now I could have a kid's head locked in my arm, choking him as I snarled at the others. Right now, instead of sweating in my pocket, my hand could have been around a young throat as I hauled the boy in a search for a police car.

I'm pretty sure I could have done it, providing all they had were cap guns.

I get home. Our babysitter Stacy is giving Ned a bath. He kicks as she holds his head above the water. Alex is rocking on his horse and watching Mother Goose. When he sees me, he gets off and toddles over with his arms out for me to pick him up. Jill says neither of them has been out of the house all day.

Jeff Stimpson, 39, lives in New York with his wife Jill and sons Alex and Edwin. He maintains JeffsLife, a site of essays, at: http://www.jeffslife.com