Dudley took it, glanced at it, and started quickly. Then he fixed his eyes upon his visitor in boundless surprise. The man before him smiled faintly at the impression which the sight of that document had caused. The paper was headed with the British arms in scarlet, and contained only three lines written over a signature he knew well--the signature of the Prime Minister of England. "And you are really Captain Cator?" exclaimed the Under-Secretary, looking at him in amazement, and handing him back his credential. "Yes, Archibald Cator, chief of Her Majesty's Secret Service," said the shrunken-faced man. "We have had correspondence on more than one occasion, but have never met, for the simple reason that I am seldom in England. Now you will at once recognise why I refused a card, and also why I wished my visit to you to remain a secret." "Of course, of course," answered Dudley. "I had no suspicion of your identity, and--well, if you will permit me to say so, your personal appearance at this moment is scarcely that which might be expected of Captain Archibald Cator, military attach in Rome." "Exactly! But I have been paying a call earlier in the day, and shabbiness was a necessity," he explained with a laugh. "Besides, I tramped all the way from Shrewsbury and--" "And you are wet and cold. You'll have a stiff whiskey and soda." Dudley pressed the bell and, when Riggs appeared, gave the necessary order. "You won't return to-night, of course," suggested Chisholm. "I'll tell them to get a room ready for you." "Thanks for your hospitality, but my return is absolutely imperative. There is a train from Shrewsbury to town at 4:25 in the morning. I must leave by that." Both men sank into chairs opposite each other in the chill, rather gloomy, room. The mysterious visitor who had called at that extraordinary hour was one of the most trusted and faithful servants at the disposal of the Foreign Office. Although nominally holding the appointment of military attach at the Embassy in Rome, he was in reality the chief of the British Secret Service on the Continent, a man whose career had been replete with extraordinary adventures, to whose marvellous tact, ready ingenuity, and careful methods of investigation, England was indebted for many of the diplomatic _coups_ she had made during the past dozen years or so.