With a slight shiver, the Prime Minister got up and moved over to the window, looking out at the thin mist that was pressing itself against the glass. It was then, as he stood with his back to the room, that he heard a soft cough behind him. He froze, nose to nose with his own scared-looking reflection in the dark glass. He knew that cough. He had heard it before. He turned very slowly to face the empty room. "Hello?" he said, trying to sound braver than he felt.