was an engineer by profession!"

The others listened to him with a sort of uneasy oppression. What was
gradually being revealed of the tragedy, instead of relieving the
anxiety, increased it until it became absolutely painful.

M. Desmalions objected:

"Granting that the letters arrived on the dates named, you will
nevertheless have noted that the hour varied on each occasion.

"That is to say, it varied according as we watched in the dark or not,
and that is just the detail which supplied me with the key to the
riddle. If the letters--and this was an indispensable precaution, which
we are now able to understand--were delivered only under cover of the
darkness, it must be because a contrivance of some kind prevented them
from appearing when the electric light was on, and because that
contrivance was controlled by a switch inside the room. There is no
other explanation possible.

"We have to do with an automatic distributor that delivers the
incriminating letters which it contains by clockwork, releasing them only
between this hour and that on such and such a night fixed in advance and
only at times when the electric light is off. You have the apparatus
before you. No doubt the experts will admire its ingenuity and confirm my
assertions. But, given the fact that it was found in the ceiling of this
room, given the fact that it contained letters written by M. Fauville, am
I not entitled to say that it was constructed by M. Fauville, the
electrical engineer?"

Once more the name of M. Fauville returned, like an obsession; and each
time the name stood more clearly defined. It was first M. Fauville; then
M. Fauville, the engineer; then M. Fauville, the electrical engineer. And
thus the picture of the "hater," as Don Luis said, appeared in its
accurate outlines, giving those men, used though they were to the
strangest criminal monstrosities, a thrill of terror. The truth was now
no longer prowling around them. They were already fighting with it, as
you fight with an adversary whom you do not see but who clutches you by
the throat and brings you to the ground.

And the Prefect of Police, summing up all his impressions, said, in a
strained voice:

"So M. Fauville wrote those letters in order to ruin his wife and the man
who was in love with her?"

"Yes."

"In that case--"

"What?"

"Knowing, at the same time, that he was threatened with death, he wished,
if ever the threat was realized, that his death should be l