ther. Haven't either of you heard the sound of a plane lately?" he
appealed to the others. "I know I haven't."

Bob and Jack both shook their heads in negation.

"No planes ever come out this way," Bob said. "They fly south or north
of us, but not out here. I haven't heard anything."

Jack rose and stretched.

"Well, I, for one, vote that we do not pursue our investigations into
this mystery by going back and, perhaps, getting peppered with
gunshot."

"But, Jack," protested Bob, the impetuous, "we want to know what's
going on. You can't have a mystery dumped right in your own dooryard
without digging into it."

Frank was thoughtful.

"That's true, Bob, old thing," he said. "Just the same, I agree with
Jack. What do you say to laying the matter before Uncle George and Mr.
Hampton at dinner? Jack and his father are coming over to our house
to-night, you know."

"Good," said Jack. "We can put it up to them, and, perhaps, they will
know something about the man who owns that land around Starfish Cove,
where this secret radio is located."

Big Bob grumbled. Delay irked his soul.

"All right, you old grumbler," laughed Frank. "Come on, I'll give you
some action. We have several hours of good daylight left before
dinnertime. I'll take you on at tennis. Della and I will play you and
Jack, and we won't give you time to worry about anything."

Della was Bob's sister, two years younger than he. Frank, whose
parents were dead and who lived with the Temples, referring to Mr.
Temple, his guardian, as "Uncle George," was very fond of her. The
others joshed him about Della frequently. Bob took occasion to do so
now, as the three walked away from the hangar toward the Temple home
and tennis courts.

"Huh," he said, "you'll be looking at your partner so often you won't
be able to play. Why, you won't even be good practice for Jack and
me."

CHAPTER III

THE HAUNTED HOUSE

Della was lithe-limbed, quick of eye and strong of wrist, a born
tennis player. As for Frank, tennis was the one sport at which he
could excel his chums. The result was that, despite the strong game
played by Jack and Bob, Frank and Della won two sets, 7-5, 8-6.

Mr. Hampton appeared on the scene when the second set stood at
six-all, bringing with him an alert, thin-faced man of middle age,
clad in the uniform of a colonel in the United States Engineers. Mr.
Temple with his wife emerged from the house to greet their guests, and
all four wer