Frost found Herb painting on his hands and knees on a sidewalk at the base of Coit Tower. Twenty people crowded behind him, watching his three-dimensional portrait take shape. A grizzly bear with wet, matted fur rose out of the flat ground. The animal, its mouth open and teeth bared, stood at the top of a surging waterfall as Herb put the final touches on a spawning salmon that was about to become the bear’s lunch.

His friend rocked back on his knees. The beads in his long gray hair knocked together like an abacus. He flipped up the magnifying lenses he wore and reached for his coffee urn. As he drank, he spotted Frost among the crowd.

“Taking a little break here, folks,” Herb announced. “Don’t get too close to the bear. He’s hungry.”

He emptied the top hat where he kept his tips and shoved the money into the pockets of his blue-jean coveralls, which were smeared with a rainbow of paint. He limped over to Frost, who held Shack in the crook of one arm. The two men walked around the perimeter of the parking lot, with the city and the bay spread out in the valley. They stopped in the shadow of the tower, across from a statue of Christopher Columbus.

“I got your message,” Herb said. “You said a girl is missing? Another one of Dr. Stein’s patients?”

“There’s a connection, yes.”

Herb took Shack from Frost’s arms. He dangled a rope of his gray hair, and Shack swiped at it. “I was disturbed to hear that someone is abducting and brainwashing these women.”

“He calls himself the Night Bird,” Frost said.

“Do you have any idea what that means?”

“Not yet.”

“If it’s someone with a grudge against Dr. Stein, then he’s part of a long list,” Herb said.

“I know that.”

“What about the girl? How long has she been gone?”

“Since last night. Jess and I interviewed the neighbors. One of them heard a scream but didn’t report it.”

“Do you have any leads?” Herb asked.

“Nothing that will help us find her. Lucy’s phone is off, so we can’t get any pings. No one saw a car in the alley where she was taken.”

“What about the person who’s doing this?”

Frost showed Herb the photograph of the mask he’d found online. “I talked to a homeless man who hangs out near Lucy’s building. Someone wearing a mask like this gave him fifty bucks to clear out for the day. The same thing happened the previous week. I think that’s when this guy took Lucy’s roommate.”

“Didn’t the man think this was odd? Money from some stranger in a mask?”