SAM HARRISON swung his agile body out of the silver blue Ford Aerostar, which he had parked on Q Street in the Georgetown section of Washington. Horror stories and games are popular for a good reason, he was thinking as he locked the vehicle and set its alarm. Not the comfortable sit-around-the-campfire horror tales and games we used to cherish as kids, but the real-life horror stories that are around us everywhere these days.

Now I'm living one myself. I'm about to become part of the horror. How easy it is. How terribly, terribly easy to move past the edge and into the darkness.

He had stalked and shadowed Daniel Fitzpatrick for two long weeks. He'd done his job in New York City, London, Boston, and finally, here in Washington, D.C. Tonight he was going to murder the United States senator. In cold blood, execution-style. No one would be able to figure out why. No one would have a clue that might matter later on.

That was the first and most important rule of the game called Jack and Jill.

In many ways this was a textbook celebrity-stalker pattern. He knew it to be true as he took up his post across from 211 Q Street.

And yet, if anyone bothered to look more closely, it was like no other stalking pattern before. What he was going to do now was more provocative than secretly observing Senator Fitzpatrick down obscene numbers of Glenlivet cocktails at The Monocle, his favorite bar in Washington. This was the truest form of madness, Sam Harrison knew. It was pure madness. He didn't believe he was mad. He believed only in the validity of the game of chance.

And then, less than thirty yards across the shiny-wet street -- there was Daniel Fitzpatrick himself. Right on schedule. At least, close enough.

He watched the senator stiffly climb out of a gleaming, navy blue Jaguar coupe, a 1996 model. He wore a gray topcoat with a paisley silk scarf. A sleek, slender woman in a black dress was with him. A Burberrys raincoat was casually thrown over her arm. She was laughing at something Fitzpatrick had said. She threw her head back like a beautiful, spirited horse. A wisp of her warm breath met the cool of the night.

The woman was at least twenty years the senator's junior. She wasn't his wife, Sam knew. Dannyboy Fitzpatrick rarely if ever slept with his wife. The blond woman walked with a slight limp, which made the two of them even more intriguing. Memorable, actually.

Sam Harrison concentrated fiercely. Measure twice, measure five times, if necessary. He took stock of all the details one final time. He had arrived in Georgetown at eleven-fifteen. He looked as if he belonged in the chic, attractive, fashionable neighborhood around Q Street. He looked exactly right for the part he was going to play.

A very big part in a very big story, one of the biggest in America's history. Or some would say American theater.

A leading-man role, to be sure.

He wore professorial, tortoiseshell glasses for the part. He never wore glasses. Didn't need them.

His hair was light blond. His hair wasn't really blond.

He called himself Sam Harrison. His name wasn't really Sam. Or Harrison.

For that night's special occasion, he'd carefully selected a soft black cashmere turtleneck, charcoal gray trousers, which were pleated and cuffed, and light-brown walking boots. He wasn't really such a dapper, self-absorbed dresser. His thick hair was cut short, vaguely reminiscent of the actor Kevin Costner in The Bodyguard, one of his least-favorite movies. He carried a small black duffel bag, swinging it like a baton as he now walked briskly toward 211. A camcorder was tucked inside the bag.

He planned to capture as much of this as possible on film. This was history in the making. It really was history: America at the end of its century, America at the end of an era, America at the end.

At quarter to twelve, he entered 211 through a darkened service entryway that smelled strongly of ammonia and of dust and decay. He walked up to the fourth floor, where the senator had his flat, his study, his love nest in the capital.

He reached Daniel Fitzpatrick's door, 4J, at ten minutes to twelve. He was still pretty much on time. So far, so good. Everything was going exactly as planned.

The highly polished mahogany door opened right in his face.

He stared at an ash-blond woman who was slender and trim and well kept. She was actually somewhat plainer looking than she had appeared from a distance. It was the same woman who had gotten out of the blue Jag with Fitzpatrick. The woman with the limp.

Except for a gold barrette in her hair, a lioness from a trip to the Museum of Modern Art in New York, and a gold choker, she was gloriously naked.

"Jack," she whispered.

"Jill," he said, and smiled.