Monsieur Lecoq, Volume I by Emile Gaboriau

It was some distance from the Poivriere to the Rue de Chevaleret, even by way of the plain, and fully four hours had been occupied by Lecoq and his colleague in collecting their elements of information.

All this while, the Widow Chupin's abode had remained open, accessible to any chance visitor. Still, when, on his return, the young police agent remembered this neglect of elementary precautions, he did not feel alarmed. Considering all the circumstances, it was very difficult to believe that any serious harm could have resulted from this carelessness.