When one of the investigating magistrates of the Tribunal of the Seine wishes to examine a person confined in one of the Paris prisons, he sends by his messenger to the governor of that particular jail a so-called “order of extraction,” a concise, imperative formula, which reads as follows: “The keeper of ---- prison will give into the custody of the bearer of this order the prisoner known as ----, in order that he may be brought before us in our cabinet at the Palais de Justice.” No more, no less, a signature, a seal, and everybody is bound to obey. But from the moment of receiving this order until the prisoner is again incarcerated, the governor of the prison is relieved of all responsibility. Whatever may happen, his hands are clear. Minute precautions are taken, however, so that a prisoner may not escape during his journey from the prison to the Palais. He is carefully locked up in a compartment of one of the lugubrious vehicles that may be often seen waiting on the Quai de l’Horloge, or in the courtyard of the Sainte-Chapelle. This van conveys him to the Palais, and while he is awaiting examination, he is immured in one of the cells of the gloomy jail, familiarly known as “la Souriciere” or the “mouse-trap.” On entering and leaving the van the prisoner is surrounded by guards; and on the road, in addition to the mounted troopers who always accompany these vehicles, there are prison warders or linesmen of the Garde de Paris installed in the passage between the compartments of the van and seated on the box with the driver. Hence, the boldest criminals ordinarily realize the impossibility of escaping from this ambulatory prison. Indeed, statistics record only thirty attempts at escape in a period of ten years. Of these thirty attempts, twenty-five were ridiculous failures; four were discovered before their authors had conceived any serious hope of success: and only one man actually succeeded in alighting from the vehicle, and even he had not taken fifty steps before he was recaptured. Lecoq was well acquainted with all these facts, and in preparing everything for May’s escape, his only fear was lest the murderer might decline to profit of the opportunity. Hence, it was necessary to offer every possible inducement for flight. The plan the young detective had eventually decided on consisted in sending an order to Mazas for May to be despatched to the Palais de Justice. He could be placed in one of the prison vans, and at the moment of starting the door of his compartment would not be perfectly secured. When the van reached the Palais de Justice and discharged its load of criminals at the door of the “mouse-trap” May would purposely be forgotten and left in the vehicle, while the latter waited on the Quai de l’Horloge until the hour of returning to Mazas. It was scarcely possible that the prisoner would fail to embrace this apparently favorable opportunity to make his escape.