The gate swings open and a man on a green motorcycle banks steeply into the lane, the two cylinders of his machine blatting away, the noise stinging Waterhouse’s nose as he rides by. Waterhouse strides after him for some distance, but loses his trail after a hundred yards or so. That is acceptable; more of them will be along soon, as the Wehrmacht’s nervous system awakens and its signals are picked up by the Y Service.