"Think of all the places that must be guarded. The waterworks,
the gas tanks, the railroads that lead to the seaports and that
will be used by the troops."

A startled burst of exclamations answered him. "Why, there won't
be any fighting in England, sir, will there?" asked Dick Mercer,
in surprise.

"We all hope not," said Grenfel. "But that's not what I mean. It
doesn't take an army to destroy a railroad. One man with a bomb
and a time fuse attached to it can blow up a culvert and block a
whole line so that precious hours might be lost in getting
troops aboard a transport. One man could blow up a waterworks or
a gas tank or cut an important telegraph or telephone wire!"

"You mean that there will be Germans here trying to hurt England
any way they can, don't you sir? asked Harry Fleming.

"I mean exactly that," said Grenfel. "We don't know this -- we
can't be sure of it. But we've got good reason to believe that
there are a great many Germans here, seemingly peaceable enough,
who are regularly in the pay of the German government as spies.
We don't know the German plans. But there is no reason, so far as
we know, why their great Zeppelin airships shouldn't come sailing
over England, to drop bombs down where they can do the most harm.
There is nothing except our own vigilance to keep these spies,
even if they have to work alone, from doing untold damage!"

'We could be useful as sentries, then?" said Leslie Franklin. He
drew a deep breath. "I never thought of things like that, sir!