"You are aware, Mr. Copplestone, that a most important part of my work consists in stopping the channels through which information of what is going on in our shipyards and munition shops may get through to the enemy. We can't prevent his agents from getting information--that is always possible to those with unlimited command of money, for there are always swine among workmen, and among higher folk than workmen, who can be bought. You may take it as certain that little of importance is done or projected in this country of which enemy agents do not know. But their difficulty is to get it through to their paymasters, within the limit of time during which the information is useful. There are scores of possible channels, and it is up to us to watch them all. You have already shown some grasp of our methods, which in a sentence may be described as unsleeping vigilance. Once we know the identity of an enemy agent, he ceases to be of any use to the enemy, but becomes of the greatest value to us. Our motto is: Ab hoste doceri." He pronounced the infinitive verb as if it rhymed with glossary. "You are quite a scholar, Mr. Dawson," remarked I politely. "Yes," said he, simply. "I had a good schooling. I need not go into details," he went on, "of how we watch the correspondence of suspected persons, but you may be interested to learn that during the three weeks which I have passed in your city all your private letters have been through my hands." "The devil they have," I cried angrily. "You exceed your powers. This is really intolerable." "Oh, you need not worry," replied Dawson serenely. "Your letters were quite innocent. I am gratified to learn that your two sons in the Service are happy and doing well, and that you contemplate the publication of another book." It was impossible not to laugh at the man's effrontery, though I felt exasperated at his inquisitiveness. After all, there are things in private letters which one does not wish a stranger, and a police officer, to read. "And how long is this outrage to continue?" I asked crossly. "That depends upon you. As soon as I am satisfied that you are as trustworthy as the local police and other authorities believe you to be, your correspondence will pass untouched. It is of no use for you to fume or try to kick up a fuss in London. Scotland Yard would open the Home Secretary's letters if it had any cause to feel doubtful of him." "You cannot feel much suspicion of me or you would not tell me what you have been doing." "You might have thought of that at once," said Dawson derisively. I shook myself and conceded the round to Dawson.