Sharon Moore's sense of danger was sudden, itching at the back of her neck as she stood on the curb to lock her car door. Although Haight Street one block away was alive with lights and activity, the side street of narrow Victorian houses was dark and shadowy. She turned quickly, her gaze darting up and down the sidewalk -- cracked and chipped concrete as old as the turn-of-the-century homes that stood braced against each other as they tilted forward onto their steep front stairways.
In the distance a woman walked her dog, and further still, a man parked a motorcycle. Neither of them even noticed that she shared the street with...