They pursued Darren down a boulevard lined with trees and wide lawns on the north side of the park. A handful of bicyclists and joggers braved the rain on the trails beside them. The sky felt low, painted in angry charcoal. On their right, they passed the Conservatory of Flowers, surrounded by palm trees and gardens. Farther on, they saw the tower of the de Young museum.

Traffic thinned. The Lexus turned onto a small road leading deep into the center of the park, and Frost lingered to give the other vehicle space, then turned behind him. Dense trees soon enveloped them on both sides.

“He’s heading for Stow Lake,” Frost said. “Maybe he’s looking for the White Lady.”

“Ghost stories, Inspector? From you?”

“At night, the lake trail can make you believe almost anything,” Frost said. “I’ve been there.”

Ahead of them, the road split. Darren followed the lake’s northeastern border. It was as if they’d left the city completely behind them. Under the trees and the gray sky, the evening felt like night. Emerald water opened up on their right. The forested slope of Strawberry Hill rose from the middle of the lake. It was a steep climb to the top, with sweeping views of the city and a peek-a-boo glimpse of the spires of the Golden Gate Bridge.

Darren’s Lexus disappeared, but he couldn’t go far on the one-way street. Frost inched along the lake road in his wake. They followed a horseshoe bend to the southern shore, where the shoulder sloped upward above them, and the water disappeared through a mass of heavy brush. Gnarled trees lined the shoulders, deepening the darkness with their tall crowns.

When they wound around the next curve, they saw Darren’s Lexus parked on the side of the road. The car was empty. Darren was already gone. Frost backed up until the Lexus was out of sight, and then he pulled his Suburban into the dirt and turned off the engine. They both got out. Rain pattered on the tree leaves above them. It was quiet, far from the city noise.

Frost walked toward Darren’s car, and Frankie followed. The loneliness of the park made her uneasy. When they reached the Lexus, Frost checked inside, but Darren had left nothing behind.

“He wasn’t dressed for jogging,” Frankie said. “So where is he?”

“He got a call. He may be meeting someone.”

Together, they climbed the slope to a lakeside hiking path. Stow Lake’s ribbon of lazy green water hugged the trail. Frost stopped to listen, but they heard no footsteps on the gravel, just rain tapping on leaves. She’d been here on summer weekends, when the lake felt as peaceful as Chopin piano music. But not now. Now the dark water under the storm felt ominous.