It was the third time in a month he had come to Los Angeles to observe her daily activities. "I know your comings and goings," he whispered as he waited in the pool house. It was one minute of seven. The morning sun was filtering through the trees, causing the waterfall that spilled into the pool to sparkle and shimmer.

He wondered if Alison could sense that she had only one minute more of life on earth. Did she have an uneasy feeling, perhaps a subconscious urge to skip her swim this morning? Even if she did, it wouldn't do her any good. It was too late.

The sliding glass door opened, and she stepped onto the patio. Thirty-eight years old, she was infinitely more attractive than she had been twenty years ago. Her body, tanned and sleek, looked good in the bikini. Her hair, now honey blond, framed and softened her sharp chin.

She tossed the towel she was carrying onto a lounge chair. The blinding anger that had been simmering inside him escalated into rage, but then, just as quickly, was replaced by the satisfaction of knowing what he was about to do. He had seen an interview in which a daredevil stunt diver swore that the moment before he began to dive, knowing that he was risking his life, was an indescribable thrill, a sensation he needed to repeat over and over again.

For me it's different, he thought. The moment before I reveal myself to them is what gives me the thrill. I know they're going to die, and when they see me, they know, too. They understand what I am going to do to them.

Alison stepped onto the diving board and stretched. He watched as she bounced softly, testing the board, then positioned her arms in front of her.

He opened the door of the pool house just as her feet lifted from the board. He wanted her to see him when she was in midair. Just before she hit the water. He wanted her to understand how vulnerable she was.

In that split second, their eyes locked. He caught her expression as she plunged into the water. She was terrified, aware that she was incapable of flight.

He was in the pool before she had surfaced. He hugged her against his chest, laughing as she flailed about, kicking her feet. How foolish she was. She should simply accept the inevitable. "You're going to die," he whispered, his voice calm, even.

Her hair was in his face, blinding him. Impatiently he shook it away. He didn't want to be distracted from the pleasure of feeling her struggle.

The end was coming. In her craving for breath, she had opened her mouth and was gulping water. He felt her final frantic effort to break away from him, then the hopelessly feeble tremors as her body began to go limp. He pressed her close, wishing he could read her mind. Was she praying? Was she begging God to save her? Was she seeing the light that people who have experienced a near-death event claim to have seen?

He waited a full three minutes before he released her. With a satisfied smile he watched as her body sank to the bottom of the pool.

It was five minutes after seven when he climbed out of the pool, pulled on a sweatshirt, shorts, sneakers, a cap, and dark glasses. He had already chosen the spot where he would leave the silent reminder of his visit, the calling card that everybody always missed.

At six minutes past seven he began to jog down the quiet street, another early morning fitness buff in a city of fitness buffs.

Sam Deegan had not intended to open the file on Karen Sommers that afternoon. He'd been fishing through the bottom drawer of his desk in search of the packet of cold pills he vaguely remembered having stashed there. When his fingers touched the well-worn and troublingly familiar folder, he hesitated and then, with a grimace, pulled it out and opened it. When he looked at the date on the first page, he realized that he had been subconsciously intending to find it. The anniversary of Karen Sommers' death was Columbus Day, twenty years ago next week.

The file ought to have been kept with the other unsolved cases, but three successive Orange County prosecutors had indulged his need to keep it at his fingertips. Twenty years ago Sam had been the first detective to arrive in response to the frantic phone call from a woman screaming that her daughter had been stabbed.

Minutes later, when he had arrived at the house on Mountain Road in Cornwall-on-Hudson, he had found the victim's bedroom crowded with shocked and horrified onlookers. One neighbor was bent over the bed uselessly trying to administer mouth-to-mouth resuscitation. Others were attempting to pull the hysterical parents away from the heartbreaking sight of their daughter's brutalized body.

Karen Sommers' shoulder-length hair was spilling onto the pillow. When he yanked the would-be rescuer back, Sam could see the vicious stab wounds in Karen's chest and heart that must have caused instant death and had drenched the sheets with her blood.

He remembered his initial thought had been that the young woman probably never even heard her attacker enter her room. She probably never woke up, he reflected, shaking his head as he opened the folder. The mother's screams had attracted not only neighbors but a landscaper and delivery man who were on the premises next door. The result was a thoroughly compromised crime scene.

There had been no signs of forced entry. Nothing was missing. Karen Sommers had been a twenty-two-year-old first-year medical student who surprised her parents by coming home for an overnight visit. The logical suspect was her ex-boyfriend, Cyrus Lindstrom, a third-year law student at Columbia. He admitted that Karen had told him she wanted both of them to start seeing other people, but he also insisted that he had agreed it was a good idea because neither one of them was ready for a serious commitment. His alibi-that he had been asleep in the apartment he shared with three other law students-was verified, although all three roommates admitted they had gone to bed by midnight and therefore did not know whether or not Lindstrom had left the apartment after that time. Karen's death was estimated to have taken place between two and three in the morning.

Lindstrom had visited the Sommers house a few times. He knew a spare key was kept under the fake rock near the back door. He knew that Karen's room was the first one to the right off the back staircase. But that wasn't proof that in the middle of the night he had driven fifty miles from Amsterdam Avenue and 104th Street in Manhattan to Cornwall-on-Hudson and killed her.

"A person of interest"-that's what we call people like Lindstrom today, Sam reflected. I always thought that guy was as guilty as sin. I could never understand why the Sommers family stood by him. God, you'd have thought they were defending their own son.

Impatiently, Sam dropped the file on his desk, got up, and walked to the window. From his perspective he could see the parking lot, and he remembered the time a prisoner on trial for murder had overpowered a guard, dropped out the window of the courthouse, raced across the lot, mugged a guy getting into his car, and driven away.

We got him in twenty minutes, Sam thought. So why in twenty years can't I find the animal who killed Karen Sommers? For my money, it's still Lindstrom.

Lindstrom was now a high-powered New York criminal attorney. He's a master at getting the murdering bums off, Sam thought. Appropriate, since he's one of them.

He shrugged. It was a rotten day, rainy and unusually cold for early October. I used to love this job, he thought, but it's not the same anymore. I'm ready to retire. I'm fifty-eight years old; I've been at police work most of my life. I should just take the pension and run. Lose a little weight. Visit the kids and spend more time with the grandkids. Before you know it, they'll be in college.