made him explain how the remedy was to be applied. He thanked the
policeman, closed the door, and went up to his room. A second later the
cord was cut at the window and quietly pulled in.

Dupré sat down and breathed hard for a few moments.

"You fool!" he said to himself; "a mistake or two like that and you are
doomed. That's what comes of thinking too much on one branch of your
subject. Another two feet and the string would have been down on his
nose. I am certain he did not see it; I could hardly see it myself,
looking for it. The guarding of the side door was an inspiration. But
I must think well over every phase of the subject before acting again.
This is a lesson."

As he went on with his preparations it astonished him to find how many
various things had to be thought of in connexion with an apparently
simple scheme, the neglect of any one of which would endanger the whole
enterprise. His plan was a most uncomplicated one. All he had to do was
to tie a canister of dynamite at the end of a string of suitable
length, and at night, before the café doors were closed, fling it from
his window so that the package would sweep in by the open door, strike
against the ceiling of the café, and explode. First he thought of
holding the end of the cord in his hand at the open window, but
reflection showed him that if, in the natural excitement of the moment,
he drew back or leant too far forward the package might strike the
front of the house above the door, or perhaps hit the pavement. He
therefore drove a stout nail in the window-sill and attached the end of
the cord to that. Again, he had to render his canister of explosive so
sensitive to any shock that he realised if he tied the cord around it
and flung it out into the night the can might go off when the string