The RAF men with the Sten guns, standing watch by each door of that train, checking papers and passes, will not let him aboard. Waterhouse looks through the yellowing influence of the windows at the Bletchley girls in the train, facing each other in klatsches of four and five, getting their knitting out of their bags, turning balls of Scottish wool into balaclavas and mittens for convoy crews in the North Atlantic, writing letters to their brothers in the service and their mums and dads at home. The RAF gunmen remain by the doors until all of them are closed and the train has begun to move out of the station. As it builds speed, the rows and rows of girls, knitting and writing and chatting, blur together into something that probably looks a good deal like what sailors and soldiers the world over are commonly seeing in their dreams. Waterhouse will never be one of those soldiers, out on the front line, out in contact with the enemy. He has tasted the apple of forbidden knowledge. He is forbidden to go anywhere in the world where he might be captured by the enemy.