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 end of a ball of twine.

About his body he had coiled a long, very thin, very strong rope.