waters of the placid river, and finally the shore. Here you notice a
train passing some little distance away, and in it, gazing out of one
of the windows, you observe--Bill, the murderer! You at once start in
pursuit; by a superb effort you catch up the train, and just succeed
in swinging yourself safely on board. You can do a little sprinting, I
suppose?"

"I could give an ordinary train a bit of a start, no doubt," said
Percy with confidence.

"Just so," pursued the producer. "And now you find yourself
confronting the miscreant, Bill. The train is passing through a city.
It is on the elevated railway. Bill makes a dash for the door, springs
out, and lands on the roof of a house. You follow him--your leap being
considerably greater, because between his jump and yours the train has
proceeded a certain distance."

"Precisely," said Percy.

"Now there is a scramble over the roof-tops. You climb up pipes, slide
down slates, leap across spaces between separate houses, cling to
coping stones, and all that sort of thing."

"I grasp the idea," said Percy.

[Illustration: "HE CUTS THE WIRES ON WHICH YOU ARE CROSSING."]

"At last Bill is seized with a notion. He throws himself on to the
telephone wires, and, hanging by his hands, manages to convey himself
across to the houses on the opposite side of the road. You imitate