HERE'S HOW TO TAKE A GANG TOUR: start at a bus parked outside a Silverlake building called The Dream Center, where grown adults cluster like kids on a field trip. Pay $65, and take your complimentary bottled water. Notice the church group from Missouri, 20-strong and blonde, and eye their grocery bag full of snacks. Notice the surprising number of Australians. They pace restlessly. One of them is named Tiny, but he isn’t. He appears to be here with his son, a teenager in baggy shorts and braces.

Alfred is the guide. He’s a marine turned gangbanger turned entrepreneur. He’s cracking Inner City Jokes. His phrase. We don’t need the windows open cuz we don’t do drive-bys. Also, we can’t have them open because the bus is air-conditioned. He’s hired three other guys to help lead the tour — ex-gang-members who had trouble finding other jobs with felonies on their records. They’ve turned their experiences into stories for travelers. They are curators and exhibits at once. When they’re not giving tours, they’re doing conflict mediation in the communities these tours put on display. The $65 will fund this work.

Your friend the screenwriter arrives. He compliments your tactful yellow dress — neither Crips blue nor Bloods red — and you remember elementary school field trips downtown. You and your fellow Westsiders were given careful instructions about gang hues. The Missouri group leader is a buzz-cut guy whom Alfred affectionately calls “Pastor.” Where’s Pastor? he says, when he’s talking about something Pastor might be interested in.

On board the bus, the jokes continue — In the event of an emergency, you’ll find bullet proof vests under your seats — but the scenery changes: Silverlake bungalows give way to the warehouses of downtown and the signage of a hybrid city — Papuserias and Pho shops, Spanglish enticements: Thrift Store Y Café. A hotline at 1-800-72-DADDY promises dads it can get them custody or at least visitation rights.

Each guide stands at the front of the bus to tell his story. One guy, let’s call him Capricorn, points out the projects where his first girlfriend still lives. “Still won’t take my calls,” he says. Another guy lays down statistics — every felony, every sentence, every prison, how much coke he got busted for each time. One guy describes a brutal turf war on the first day of junior high, when the kids from three different elementary schools — each one loyal to a different gang — were all jammed together for the first time. They started clapping at each other until the police came. You think clapping is a kind of hand signal. You learn it’s not. Guys get their first guns when they’re eleven, you’re told. Moms don’t ask where the money comes from.

You hear notes of something like nostalgia when these guys talk about their former lives — the weapons and arrests, the monstrous tallies of their former cash flows. Pride comes before the fall and also after it. But the nostalgia is tangled up with a deep and genuine lamenting of the terms of this territory--how harshly it circumscribes the path, how inevitably it punishes alternatives. For these guys, though, things are different now. They got out of prison and wanted another way. When Alfred says, I’m a spiritual man, you see him looking around to see if Pastor’s listening. H...