"All my congratulations, dear sir and dear friend, on your arrest of Jérôme the messenger. It was a smart piece of work, well executed and worthy of you. "All my compliments, also, on the ingenious manner in which you proved to the prime minister that I was not Mr. Kesselbach's murderer. Your demonstration was clear, logical, irrefutable and, what is more, truthful. As you know, I do not kill people. Thank you for proving it on this occasion. The esteem of my contemporaries and of yourself, dear sir and dear friend, are indispensable to my happiness. "In return, allow me to assist you in the pursuit of the monstrous assassin and to give you a hand with the Kesselbach case, a very interesting case, believe me: so interesting and so worthy of my attention that I have determined to issue from the retirement in which I have been living for the past four years, between my books and my good dog Sherlock, to beat all my comrades to arms and to throw myself once more into the fray. "What unexpected turns life sometimes takes! Here am I, your fellow-worker! Let me assure you, dear sir and dear friend, that I congratulate myself upon it, and that I appreciate this favor of destiny at its true value. "ARSÈNE LUPIN. "P.S.--One word more, of which I feel sure that you will approve. As it is not right and proper that a gentleman who has had the glorious privilege of fighting under my banner should languish on the straw of your prisons, I feel it my duty to give you fair warning that, in five weeks' time, on Friday, the 31st of May, I shall set at liberty Master Jérôme, promoted by me to the rank of chief messenger at the Ministry of the Interior. Don't forget the date: Friday, the 31st of May. "A. L." CHAPTER IV PRINCE SERNINE AT WORK A ground-floor flat, at the corner of the Boulevard Haussmann and the Rue de Courcelles. Here lived Prince Sernine: Prince Sernine, one of the most brilliant members of the Russian colony in Paris, whose name was constantly recurring in the "Arrivals and Departures" column in the newspapers. Eleven o'clock in the morning. The prince entered his study. He was a man of thirty-eight or forty years of age, whose chestnut hair was mingled with a few silver threads on the temples. He had a fresh, healthy complexion and wore a large mustache and a pair of whiskers cut extremely short, so as to be hardly noticeable against the fresh skin of his cheeks. He was smartly dressed in a tight-fitting frock-coat and a white drill waistcoat, which showed above the opening. "Come on!" he said, in an undertone. "I have a hard day's work before me, I expect." He opened a door leading into a large room where a few people sat waiting, and said: