ebble at
the nineteenth metre and flung it toward the land side. The pebble at
most reached the end of the path.

"Idiot that I am!" thought Beautrelet. "Who reckoned by metres in those
days? The figure 19 means 19 fathoms[9] or nothing!"

[9] The toise, or fathom, measured 1.949 metres.--Translator's Note.

Having made the calculation, he ran out the twine, made a knot and felt
about on the piece of wall for the exact and necessarily one point at
which the knot, formed at 37 metres from the window of the Demoiselles,
should touch the Frefosse wall. In a few moments, the point of contact
was established. With his free hand, he moved aside the leaves of
mullein that had grown in the interstices. A cry escaped him. The knot,
which he held pressed down with his fore-finger, was in the centre of a
little cross carved in relief on a brick. And the sign that followed on
the figure 19 in the document was a cross!

It needed all his will-power to control the excitement with which he
was overcome. Hurriedly, with convulsive fingers, he clutched the cross
and, pressing upon it, turned it as he would have turned the spokes of
a wheel. The brick heaved. He redoubled his effort; it moved no
further. Then, without turning, he pressed harder. He at once felt the
brick give way. And, suddenly, there was the click of a bolt that is
released, the sound of a lock opening and, on the right of the brick,
to the width of about a yard, the wall swung round on a pivot and
revealed the orifice of an underground passage.

Like a madman, Beautrelet seized the iron door in which the bricks were
sealed, pulled it back, violently and closed it. Astonishment, delight,
the fear of being surprised convulsed his face so as to render it
unrecognizable. He beheld the awful vision of all that had happened
there, in front of that door, during twenty centuries; of all those
people, initiated into the great secret, who had penetrated through
that issue: Celts, Gauls, Romans, Normans, Englishmen, Frenchmen,
barons, dukes, kings--and, after all of them, Arsene Lupin--and, after
Lupin, himself, Beautrelet. He felt that his brain was slipping away
from him. His eyelids fluttered. He fell fainting and rolled to the
bottom of the slope, to the very edge of the precipice.

* * * * *

His task was done, at least the task which he was able to accomplish
alone, with his unaided resources.

That evening, he wrote a long lette