Staff Sergeant Walker steps away from the Ridgeback, wipes sweat from his eyes with a dust-grimed bandana, and tries to make sense of the scene before him. The heat has grown punishing. For a moment it twists the air, so that grey walls and desiccated bushes and sun-scorched faces above dark shalwar kameez all shiver unsettlingly. Walker wipes his eyes again and gradually the shimmering steadies. Yet still, the prospect doesn’t quite add up.