t?" asked Bob, and the
radio inspector nodded.

"In case of war," he said slowly, "I imagine these airplane-controlled
tanks could do considerable damage."

Their guest left soon after that, and, of course, the boys were sorry to
have him go. His last words to them were about Cassey.

"Keep your eyes open for that scoundrel," he said, "and we'll find out
what he's up to yet."

But in the next few days so many alarming things happened that the boys
had little time to think about Dan Cassey. The alarming happenings
consisted of a series of automobile robberies in neighboring towns,
robberies committed so skillfully that no hint nor clue was given of the
identity of the robbers.

And then the robberies came nearer home, even into Clintonia itself. The
president of one of the banks left his machine outside the bank for half
an hour, and when he came out again it was gone. No one could remember
seeing any suspicious characters around.

Then Raymond Johnston, a prominent business man of the town, had his car
taken in the same mysterious manner from in front of his home. As
before, no one could give the slightest clue as to the identity of the
thieves.

The entire community was aroused and the police were active, and yet the
mystery remained as dark as ever.

Then, one day, Herb came dashing over to Bob's home in a state of wild
excitement. Joe and Jimmy were already there, and Herb stopped not even
for a greeting before he sprang his news.

"Say, fellows!" he cried, sprawling in a chair and panting after his
run, "it's time somebody caught those auto thieves. They are getting a
little too personal."

"What's up?" they demanded.

"One of dad's trucks has been held up!" gasped Herb. "In broad daylight,
too!"

"Was anything taken?" asked Joe.

"Anything? Well, I should say! They looted the truck of everything. It's
a wonder they didn't steal the machinery."

"That's a pretty big loss for your dad, isn't it?" said Bob gravely.

"It is!" replied Herb, running his fingers through his hair. "He's all
cut up about it and vows he'll catch the ruffians. Though he'll have to
be a pretty clever man if he does, I'll say."

"They do seem to be pretty slick," agreed Bob.

"I wonder if the same gang is responsible for all the robberies," put in
Joe.

"It looks that way," said Jimmy. "It looks as if there were a crook at
the head of the bunch who has pretty good brains."

"A regular master criminal, Doughnuts?" gibed