We turn the corner onto San Julian Street, one of skid row's many outdoor drug parlors. At a drop-in center, he finds a shriveled 51-year-old man named Anton "Tony" Montgomery, who appears to be at death's door. He's got AIDS. He can't breathe.
"His T-cells are gone," Mack says, telling Montgomery he's got to take care of himself.
A 23-year-old woman recognizes Mack and rushes toward him, eager to answer his HIV-risk questionnaire. Yes, Nicole says, she's had sex recently, and suicidal tendencies and thoughts, and she smoked crack last night.
Mack asks how much.
"Too much and not enough," she says, drifting into incoherent scats before fluttering away like a frightened butterfly.
Back on the street, a barefoot woman rolls around on the pavement, wrestling demons in a death match. She sits up in mortal agony, her body caked with filth, her breasts exposed.
"It's poison," Mack says of the crack that devours these people. "It's not no cocaine the way it used to be." The way it was when he was hooked. You used to get it in powder form and rock it with baking soda, he says. It wasn't this pre-rocked stuff that's out here now. Who knows where it's from or what it's got in it?
"I smoked cocaine from 1979 to 2000," Mack tells me on 7th Street, and I understand his true value to this mission.
People here don't see just Christopher Mack the outreach worker. He's Christopher Mack the former addict who picked himself up and made it. For everyone out here, he's the hope.
"They had me dead to rights," Mack says of the event that turned him around. He was caught in Inglewood, picked up with cocaine on him. It was a second offense, and he was looking at five years in jail when he had a spiritual reckoning.
He heard a voice: "Someone told me, 'You won't see one day in prison.' I been clean and sober ever since."
It's just people out here, he says, wiping away tears. People who got hooked the way he did.
We make a turn and come upon the place where he last saw his brother, an addict, not too many months ago.
"He had just taken a blast. I hugged him and he called me his angel. He died in MacArthur Park three weeks later."
We walk another block and duck into an Alcoholics Anonymous meeting, 40 people gathered around a table and ready to go cold turkey. Mack introduces a recovering friend who's now helping others out of addiction.
"He's a part of my hope," Mack says.
"How are you?" a woman asks, walking past him.
"Blessed," Mack says. "And you?"