mself before that lighted window
for even the moment of a swift descent, might well be fatal. That was
one point, but he speedily devised a way of overcoming that.

There was another danger to be considered, and it took him longer to
calculate this. Naturally there was a patrol about the house. Fred
himself had had to avoid the sentry, making his steady round. Now he lay
in the bushes and timed the man's appearances for nearly half an hour.
There were two men, as a matter of fact, and they met on each circling
of the house. Fortunately, their meeting came at the very end of the
garden. So Fred was able to work out a sort of mental chart of their
movements, and to confirm it by timing them. The two sentries met on his
side of the house at the eastern end. The first walked west, the second
north. The one who walked west had his back to Fred and to the window
where Boris waited for a minute. Then he, too, turned north. Then came a
blessed interval of just a minute, in which neither sentry was in sight.
Altogether, there was a period of almost two minutes in which no eye
would be fixed on Boris's window, unless the sentry chanced to turn and
look back.

To make sure, Fred studied both men. And not once did either of them
look back or up. Their attention did not seem to centre on the house at
all. It was as if their instructions were more to prevent a surprise
attack from outside, or the coming of some spy, than to watch those who
were already in the house.

Once he had made up his mind, Fred buried himself deeper in the
shrubbery and risked using his pocket flashlight while he wrote a note
to Boris, telling him what he had learned of the movements of the
sentries. He told Boris, also, not to draw up the rope at once, but to
climb from his window to the flat roof, something easy enough to manage,
and then to move along five paces. There the rope, when it was drawn up,
would be invisible against the grey stone of the house wall, whereas,
against a lighted window, it would show up so plainly that the most
stupid sentry would be sure to see it.

Fred had substituted a tennis ball for the stone he had originally
intended to throw. The ball had many advantages. In case his aim was
bad, the ball would not make a noise if it fell or if it struck against
the wall, while the sound of a stone would have betrayed them had he
failed to put it through the window. Now he tied his note to the ball,
making it firm and secure with the en