from time to time," replied
Chief Waller. "And after the thing had been successfully done, he could
watch the two thieves gathering the swag together, and putting it in a
satchel they found in the cashier's room. Then, just at a quarter to
three they doused the glim, which was only an electric torch one of them
carried, and skipped out, locking the door on poor Cadger. It was hours
afterwards when the day watchman came on duty and the discovery
followed."

Frank and Andy had somehow turned, and exchanged a significant look
about this time; and the expression of astonishment on the face of the
latter deepened.

"Did you say an electric torch, Chief?" demanded Frank, immediately.

"Yes, one of the handy kind that are used so commonly now," the other
replied.

"Tell us, did Cadger say anything about the thieves wearing masks over
their faces; or did they use handkerchiefs to hide them from him?"

"I didn't mention that matter, but it was just as you say, Frank; both
men had on masks all the time," answered the police officer.

"Black ones too, I expect?" ventured Andy.

"That's what they were; but see here, are you two just guessing this, or
do you happen to know something about those men?" asked the other,
quickly; for he could not help seeing from the manner of the Bird boys
that they were on some sort of a scent; and he knew from past
experiences that their sagacity could always be trusted to do the right
thing.

"Well," Frank went on to say, drily, "while Andy was watching our new
hydroplane out in the Quackenboss pasture, I worked until eleven o'clock
in our shop, and then went home. This morning, early, after a bite to
eat, I hurried over there to do some finishing touches and carry the
thing out to apply to our broken plane, when to my astonishment I found
that the shop had been broken into later in the night, as well as our
hangar, where the aeroplane is usually kept. And here's what I
discovered lying on the work-bench, where the men had forgotten them."

With these words he held up the flashlight torch, and the twin black
masks; and they produced an immediate shock upon the Chief of Police.

"And you found those things in your workshop this morning, you say?"
he cried, reaching out to take hold of the torch, and the bits of black
muslin.

"Yes, and whoever was there, they must have been mad because they didn't
find the aeroplane, for they smashed a few things, just for spite, it
looked like," was wh