Evening. A typical American town. On Catoctin Mountain, a ridge of the Appalachians that runs north to south through the western part of the state, the trees were brightening into soft yellows and golds. Teenagers drove their pickup trucks slowly along the streets of the town, looking for something to happen, wishing that the summer had not ended. Faint smells of autumn touched the air, the scent of ripening apples, a sourness of dead leaves, cornstalks drying in the fields. In the apple groves at the edge of town, flocks of grackles settled into the branches for the night, squawking. Headlights streamed north on the Gettysburg road. In the kitchen of a Victorian house near the center of town, Major Nancy Jaax, a veterinarian in the United States Army, stood at a counter making dinner for her children. She slid a plate into the microwave oven and pushed a button. Time to nuke up some chicken for the kids. Nancy Jaax wore sweatpants and a T-shirt, and she was barefoot. Her feet had calluses on them, the result of martial-arts training.