Dupre kept his appointment, and the _concierge_ showed him over
the house. The back rooms were too dark, the windows being but a few
feet from the opposite wall. The lower front rooms were too noisy.
Dupre said that he liked quiet, being a student. A front room on the
third floor, however, pleased him, and he took it. He well knew the
necessity of being on good terms with the _concierge_, who would
spy on him anyhow, so he paid just a trifle more than requisite to that
functionary, but not enough to arouse suspicion. Too much is as bad as
too little, a fact that Dupre was well aware of.

He had taken pains to see that his window was directly over the front
door of the cafe, but now that he was alone and the door locked, he
scrutinised the position more closely. There was an awning over the
front of the cafe that shut off his view of the pavement and the
policeman marching below. That complicated matters. Still he remembered
that when the sun went down the awning was rolled up. His first idea
when he took the room was to drop the dynamite from the third story
window to the pavement below, but the more he thought of that plan the
less he liked it. It was the sort of thing any fool could do, as the
policeman had said. It would take some thinking over. Besides, dynamite
dropped on the pavement would, at most, but blow in the front of the
shop, kill the perambulating policeman perhaps, or some innocent
passer-by, but it would not hurt old Sonne nor yet the _garcon_
who had made himself so active in arresting Hertzog.

Dupre was a methodical man. He spoke quite truly when he said he was a
student. He now turned his student training on the case as if it were a
problem in mathematics.

First, the dynamite must be exploded inside the cafe. Second, the thing
must be done so deftly that no suspicion could fall on the perpetrator.
Third, revenge was no revenge when it (A) killed the man who fired the
mine, or (B) left a trail that would lead to his arrest.

Dupre sat down at his table, thrust his hands in his pockets, stretched
out his legs, knit his brows, and set himself to solve the conundrum.
He could easily take a handbag filled with explosive material into the
cafe. He was known there, but not as a friend of Hertzog's. He was a
customer and a tenant, therefore doubly safe. But he could not leave
the bag there, and if he stayed with it his revenge would rebound on
himself. He could hand the bag to the waiter saying he w