A young blond woman ran along a quiet tree-lined Bel-Air street at dusk. She kept her head up and her steps even and strong. The street was in the flat part of Bel-Air just north of Sunset, a neighborhood with big old houses built as mansions by movie and television people in the 1950s and '60s. Mansions still occupied giant parcels sectioned into lawns and gardens, but over time the old owners had died, and the new owners had noticed that the houses were not the newest styles and not as large as a house might be. For years they had been in the process of demolishing the old homes to build new ones that looked to them like clearer embodiments of wealth and potency.

The runner's name was Elle Stowell. She wore a dark blue T-shirt that said YALE on it and black running shorts. On her feet was a pair of distinctive running shoes of a brand worn by female runners who lived in neighborhoods like this one. They cost hundreds of dollars and were superbly made, but their real purpose was to give their wearer an edge that was more sociological than athletic. They were a credential, proof that the runner belonged here.

Elle was small, an inch over five feet tall. Her size and her pretty face made her seem younger. She was very fit, her body thinner and more long-muscled than an Olympic gymnast's because her daily routines relied more on running and swimming than on jumping and upper-body work.

Elle Stowell needed to be physically exceptional but needed not to look physically exceptional. She had to be able to show up in neighborhoods like this one looking like the daughter of the couple down the street. She often put on a shirt with the name of a university so she would appear to be a student home for a visit and running near her parents' house.

She had a light complexion and blue eyes, and she spent lots of money on styling and dyeing her hair to duplicate the golden look of the daughters of the rich. She acknowledged that she did not compare with her best friend, Sharon, who could walk into a restaurant and cause the conversations at tables to trail off, or her friend Ricki, who was a model and appeared to be an elongated ink drawing of a goddess. If pressed, Elle might have admitted she was cute.

A week ago she had driven through this neighborhood looking for the right house, and then three days later, she had walked her friend Elizabeth's little white French bulldog through here on a leash. At each house where a dog lived, the dog would charge to the fence and bark at the French bulldog, warning it to stay away forever or face dire consequences. When she had finished the walk, the bulldog felt flattered by the attention, and Elle knew where there were dogs and where there weren't. At the place she was going there weren't.

Elle needed money right now, but she didn't like working after dark, when the danger increased. Her work required her to look rich and be where rich people lived, but she was careful to tone down her appearance to avoid being kidnapper bait — no sparkly jewelry, no watch or rings, no daydreaming, particularly at night. She never let her alertness lapse, and she listened for cars overtaking her from behind. Even if there was nothing to be afraid of, no attention was welcome. Her only accessory was at her waist: a black fanny pack which contained a few small tools and a lot of empty space.

She reached the block she had chosen and ran straight to a house that was undergoing a thorough renovation. She was sure that, when completed, it would look a lot like an old gray stone bank. It had a long front porch with four pillars that appeared to hold up the front end of the roof but were only ornaments. At this stage of construction the house was surrounded by scaffolds: three levels of steel piping with walkways consisting of two ten- inch-wide boards laid side by side every three or four yards.

Elle veered in front of the building, already pulling on her surgical gloves, and hoisted herself up on the temporary chain- link fence, stepped on the chain and padlock that held the gate shut, and jumped to the ground inside the fence. She went to the scaffold on the side of the house, pulled herself up onto the first level about six feet up, and walked along the scaffolding, feeling a slight springy bounce of the boards under her feet. It occurred to her that if her 105 pounds made the boards bow a little and rebound upward, a carpenter who weighed twice as much must have a pretty bouncy walk.

She kept turning her head to look over the tall concrete fence a few feet from the scaffold. She kept looking in the windows of the house next door and seeing things that pleased her. There were no lights on in the rooms she passed. In the kitchen, the timers on the oven and the microwave, and the lighted green dots showing that the refrigerator was working, were the only signs that the power was on.

When she reached the back end of the board walkway, she shinnied up a vertical pipe of the scaffold. She was hot from running, and the coolness of the metal felt good on her legs, which were doing most of the work of pushing her body upward. She reached the second level and kept going to the third. The top level of the scaffold jutted about two feet above the eaves of the house, so she had an unobstructed view of this side of the peaked roof, a bit of the terrain beyond, and the tree canopy that shaded the quiet street for a distance on both sides. Dusk had now faded to darkness, and she could see strings of streetlights going on throughout the neighborhood.

She spent a few more minutes looking at the house next door. That house was not under renovation. She could see enough of it to verify that it was still in pristine shape from its own rebuilding a year or two ago. She could also see that the swimming pools — one big irregular-shaped pool and a long strip of water near it for swimming laps — were covered with black plastic sheeting. The nets were off the tennis courts. Days ago she had already verified that no dog was present, the cars were locked in the garage, and the newspapers and mail had been stopped.

Elle knew a lot about houses and about the ways people in rich neighborhoods thought about them. At the moment when the people living next door had learned that the house on the lot where she was standing right now was going to be razed and this monstrous building erected in its place, they had undoubtedly begun to make plane reservations. They had gone somewhere to wait out the long period of construction. If they were rich enough to afford a massive house in Bel-Air, they didn't have to sit in it and listen to the sounds of bulldozers, saws, cement trucks, nail guns, and foremen shouting at their crews in Spanish. They had, as rich people could do, sidestepped the unpleasantness. Right now they might be in the South of France or on the New England coast or touring Iceland.

Elle bent down, picked up the end of one of the boards forming the walkway of the scaffold, propped it on the scaffold's railing, and eased it across the empty space to rest on the railing of the balcony extending from the house next door. She wiggled the board to be sure that it was solidly and evenly resting on the two railings. Then she opened her fanny pack to take out a bungee cord, wrapped it around the board twice, and used the two metal hooks to secure it to the scaffold so the board would not move.

She lifted herself to the level of the railing, set a foot onto the board, and then began to...