doors
opened and all the electric lights on.

Mazeroux objected:

"It has to be dark for the letter to come. You will remember, Monsieur le
Prefet, that the other experiment was tried before and the letter was not
delivered."

"We will try it again," replied M. Desmalions, who, in spite of
everything, was really afraid of Don Luis's interference, and increased
his measures to make it impossible.

Meanwhile, as the night wore on, the minds of all those present became
impatient. Prepared for the angry struggle as they were, they longed for
the opportunity to show their strength. They made desperate use of their
ears and eyes.

At one o'clock there was an alarm that showed the pitch which the nervous
tension had reached. A shot was fired on the first floor, followed by
shouts. On inquiry, it was found that two detectives, meeting in the
course of a round, had not recognized each other, and one of them had
discharged his revolver in the air to inform his comrades.

In the meantime the crowd outside had diminished, as M. Desmalions
perceived on opening the garden gate. The orders had been relaxed and
sightseers were allowed to come nearer, though they were still kept at a
distance from the pavement.

Mazeroux said:

"It is a good thing that the explosion is due in ten days' time and not
to-night, Monsieur le Prefet; otherwise, all those good people would be
in danger as well as ourselves."

"There will be no explosion in ten days' time, any more than there will
be a letter to-night," said M. Desmalions, shrugging his shoulders. And
he added, "Besides, on that day, the orders will be strict."

It was now ten minutes past two.

At twenty-five minutes past, as the Prefect was lighting a cigar, the
chief detective ventured to joke:

"That's something you will have to do without, next time, Monsieur le
Prefet. It would be too risky."

"Next time," said M. Desmalions, "I shall not waste time in keeping
watch. For I really begin to think that all this business with the
letters is over."

"You can never tell," suggested Mazeroux.

A few minutes more passed. M. Desmalions had sat down. The others also
were seated. No one spoke.

And suddenly they all sprang up, with one movement, and the same
expression of surprise.

A bell had rung.

They at once heard where the sound came from.

"The telephone," M. Desmalions muttered.

He took down the receiver.

"Hullo! Who are you?"

A voice answered, but so dista