l astride the fuselage.

"Hello," he called. "We saw you fall and came over to see if we could
help. Engine gone wrong, or what was it?"

Higginbotham was rapidly recovering his senses. He stared at his
interlocutor keenly, then at the others. Recognition dawned, then
dismay, in his eyes. But he cloaked the latter quickly.

"Why, aren't you the lads who were in my office to-day?" he asked,
ignoring Bob's proffer of help.

"You're Mr. Higginbotham, aren't you?" answered Bob. "Yes, we are the
fellows you spoke to."

"What in the world are you doing out here?" Higginbotham demanded,
sharply.

"Why, we told you we lived near here. We had flown to Mineola and then
motored to the city. And we were just flying home when we saw you
fall, and came over to do what we could."

"Oh."

Higginbotham stared from one to the other. Had he seen them pursue him
and spy on him as he visited the schooner? That was the question each
boy asked himself. Apparently, he had not done so, for his next
question was:

"Do you fly around here often in your plane?"

Frank took a hand in the conversation. If big Bob were left to carry
on alone, he might blunderingly give this man an inkling of what the
boys knew or suspected about their mysterious neighbors. Frank felt
that his chill of suspicion, experienced when he encountered
Higginbotham in New York, was being justified. Decidedly, this man
must be in with the mysterious inhabitant of the old Brownell place.
Equally certain was it that he had lied in stating he did not know the
name of the man who had bought the property.

"Oh," said Frank, "we haven't had the plane out for weeks until a day
or two ago, when we made a trial spin, and again to-day. We've been
busy for a month overhauling it."

That, thought Frank, ought to stave off Higginbotham's suspicions.
Evidently, the other was feeling around to learn whether they had
flown sufficiently of late to have spied out the secret radio plant or
seen the radio-controlled plane in operation.

"And I'll bet," Frank said himself, "that it is a complete surprise to
him to find there is a plane in his neighborhood. Probably, he thought
he could operate without fear of discovery in this out-of-the-way
neighborhood, and it's a shock to him to find we are here."

Some such thoughts were passing through Higginbotham's mind. How could
he get rid of these boys without disclosing to them that his was a
radio-controlled plane?

"I'm very much