A little light was therefore being shed on the darkness of the Mornington case.  But, on the other hand, how inconceivable was the mystery of that letter found on the table in the workroom!

Five men had kept watch, five of the smartest men obtainable; and yet, on that night, as on the night of the fifteenth of April, an unknown hand had delivered the letter in a room with barricaded doors and windows, without their hearing a sound or discovering any signs that the fastenings of the doors or windows had been tampered with.

The theory of a secret outlet was at once raised, but had to be abandoned after a careful examination of the walls and after an interview with the contractor who had built the house, from Fauville’s own plans, some years ago.

It is unnecessary once more to recall what I may describe as the flurry of the public.  The deed, in the circumstances, assumed the appearance of a sleight-of-hand trick.  People felt tempted to look upon it as the recreation of some wonderfully skilful conjurer rather than as the act of a person employing unknown methods.

Nevertheless, Don Luis Perenna’s intelligence was justified at all points, for the expected incident had taken place on the twenty-fifth of April, as on the fifteenth.  Would the series be continued on the fifth of May?  No one doubted it, because Don Luis had said so and because everybody felt that Don Luis could not be mistaken.  All through the night of the fifth of May there was a crowd on the Boulevard Suchet; and quidnuncs and night birds of every kind came trooping up to hear the latest news.

The Prefect of Police, greatly impressed by the first two miracles, had determined to see the next one for himself, and was present in person on the third night.

He came accompanied by several inspectors, whom he left in the garden, in the passage, and in the attic on the upper story.  He himself took up his post on the ground floor with Weber, Mazeroux, and Don Luis Perenna.

Their expectations were disappointed; and this was M. Desmalions’s fault.  In spite of the express opinion of Don Luis, who deprecated the experiment as useless, the Prefect had decided not to turn off the electric light, so that he might see if the light would prevent the miracle.  Under these conditions no letter could appear, and no letter did appear.  The miracle, whether a conjuring trick or a criminal’s device, needed the kindly aid of the darkness.

There were therefore ten days lost, always presuming that the diabolical postman would dare to repeat his attempt and produce the third mysterious letter.

* * * * *

On the fifteenth of May the wait was renewed, while the same crowd gathered outside, an anxious, breathless crowd, stirred by the least sound and keeping an impressive silence, with eyes gazing upon the Fauvilles’ house.

This time the light was put out, but the Prefect of Police kept his hand on the electric switch.  Ten times, twenty times, he unexpectedly turned on the light.  There was nothing on the table.  What had aroused his attention was the creaking of a piece of furniture or a movement made by one of the men with him.