His arms, extended to break his fall, sank to the elbows in cold mud. He landed in a shallow, marshy edge of the lake. He pulled out one arm and tried to raise himself. But before he could stand, his feet slid out from under him again. This time his face went into the water and his mouth filled with foul, slimy muck. He spit it out and, bracing himself above the surface, pushed backward in a squat. His shoes, under water, found a solid base. Rising cautiously, he climbed back toward the trail. With the back of his hands, he wiped the mud from his face and walked along the footpath, shoes sloshing with every step.

He felt like an idiot. Why did he keep returning? If it was to punish himself, as the department therapist said, he’d certainly managed to do that tonight. But that explanation never felt true to Mahler—more like something the therapist formulated so she could close out their sessions. But he also couldn’t kid himself that these journeys to the park were related to any ongoing homicide investigation. No clues awaited him here.

After a hundred yards, he found the place. The trail opened to a clearing, with a large, flat rock on one side. Two years ago, the second victim, Susan Hart, had been murdered here. The evidence indicated she stopped and, with music in her earbuds, had not heard the killer’s approach.

Mahler eased onto the rock, stuffing his hands in his jeans pockets to ward off the cold. He visualized the victim’s body, facedown, at the base of the rock. Susan Hart’s right arm was stretched out, the left under her chest. The awkward, unprotected, face-forward landing of an unconscious person. Tank top, running shorts, sweatshirt, ankle socks, sneakers. A bruise on the left side of her face where it struck the ground. A small, tight pattern of loose soil and dry leaves made by the feet of the girl and her attacker in the last seconds of her life. One of the techs said it looked like a dancer’s box-step diagram.

As Mahler pictured the victim, Susan Hart’s now-familiar voice sounded in his ear. “Ever figure out what song I was listening to when I was killed?” the dead girl asked.

“No,” Mahler said. “Your phone kept playing after you died. You had something like four hundred songs.”

“What’s your guess?”

“Kenny Loggins. ‘Footloose.’”

She laughed. “Good song but old-school. No—Katy Perry. ‘Waking Up in Vegas.’ All-time favorite running song. Perfect for middle distance—sixteen hundred meters. You know I won leagues my senior year? At the junior college, I took four-tenths off my best time. You ever run, Eddie?”

“Little in high school. Cross-country.”

“Figures. Cross-country runners are brooders. No time for brooding in the sixteen hundred. Three and a half times around the track. Basically a prolonged sprint. Difficult, mentally.”

“I thought all races were mental.”