At about eleven o’clock in the evening of the 20th of February, 186 - which chanced to be Shrove Sunday, a party of detectives left the police station near the old Barriere d’Italie to the direct south of Paris. Their mission was to explore the district extending on the one hand between the highroad to Fontainebleau and the Seine, and on the other between the outer boulevards and the fortifications.