" I’VE NEVER BEEN so sad to be right," Olivia said to Sokolov, when she found him pushing a cart down an aisle in the camping and outdoors section. She fell in step next to him and cast an eye over the contents of his cart, wondering whether this was totally random stuff that he had thrown in there to perfect his Walmart shopper disguise or things he actually intended to buy: 5.56-millimeter cartridges, a water purification device, jerky, bug repellent, a camouflage hat, heavy mittens. Freeze-dried meals. A roll of black plastic sheeting. Parachute cord. Batteries. A folding bucksaw. Camouflage binoculars.