ern
suburban section, and once he had seen a maze of railway tracks that meant,
he was almost sure, that they were passing near Willisden Junction. Only a
few houses appeared in the section through which the cab was now racing,
and pavements were not frequent. He spoke to Dick in a whisper.

"There's something funny here," he said. "But, no matter what happens,
pretend you think it's all right. Let anyone who speaks to us think we're
foolish--it'll be easier for us to get away then. And keep your eyes wide
open, if we stop anywhere, so that you will be sure to know the place
again!"

"Right!" said Dick.

Just then the cab, caught in a rutty road where the going was very heavy,
and there was a slight upgrade in addition, to make it worse, slowed up
considerably. And Dick, looking out of the window on his side, gave a
stifled exclamation.

"Look there, Harry!" he said. "Do you see the sun flashing on something on
the roof of that house over there? What do you suppose that is?"

"Whew!" Harry whistled. "You ought to know that, Dick! A heliograph--field
telegraph. Morse code--or some code--made by flashes. The sun catches a
mirror or some sort of reflector, and it's just like a telegraph
instrument, with dots and dashes, except that you work by sight instead of
by sound. That _is_ queer! Try to mark just where the house is, and so will
I."

The cab turned, while they were still looking, and removed the house where
the signalling was being done from their line of vision. But in a few
moments there was a loud report that startled both scouts until they
realized that a front tire had blown out. The driver stopped at once, and
descended, seemingly much perturbed. And Harry and Dick, piling out to
inspect the damage, started when they saw that they had stopped just
outside the mysterious house.

"I'll fix that in a jiffy," said the driver, and began jacking up the
wheel. But, quickly as he stripped off the deflated tire, he was not so
quick that Harry failed to see that the blow-out had been caused by a
straight cut--not at all the sort of tear produced by a jagged stone or a
piece of broken glass. He said nothing of his discovery, however, and a
moment later he looked up to face a young man in the uniform of an officer
of the British territorial army. This young man had keen, searching blue
eyes, and very blond hair. His upper lip was closely shaven, but it bore
plain evidence that within a few days it had sported a mou