to where he had come from.

"What's the matter?" asked his father in a whisper. "What's up, Tom?"

The lad did not answer Mr. Swift, with a worried look on his face,
followed his son. Mr. Sharp stood in the door of the shop.

"I thought I heard some one moving around back here," went on Tom
quietly.

"Some one in this shop!" exclaimed the aged inventor excitedly. "Some
one trying to steal my ideas again! Mr. Sharp, come here! Bring that
rifle! We'll teach these scoundrels a lesson!"

Tom quickly darted hack to the extreme rear of the building. There was
a scuffle, and the next minute Tom cried out:

"What are you doing here?"

"Ha! I beg your pardon," replied a voice. "I am looking for Mr. Barton
Swift."

"My father," remarked Tom. "But that's a queer place to look for him.
He's up front. Father, here's a man who wishes to see you," he called.

"Yes, I strolled in, and seeing no one about I went to the rear of the
place," the voice went on. "I hope I haven't transgressed."

"We were busy on the other side of the shop, I guess," replied Tom, and
he looked suspiciously at the man who emerged from the darkness into
the light from a window. "I beg your pardon for grabbing you the way I
did," went on the lad, "but I thought you were one of a gang of men
we've been having trouble with."

"Oh, that's all right," continued the man easily. "I know Mr. Swift,
and I think he will remember me. Ah, Mr. Swift, how do you do?" he
added quickly, catching sight of Tom's father, who, with Mr. Sharp, was
coming to meet the lad.

"Addison Berg!" exclaimed the aged inventor as he saw the man's face
more plainly. "What are you doing here?"

"I came to see you," replied the man. "May I have a talk with you
privately?"

"I--I suppose so," assented Mr. Swift nervously. "Come into the house."

Mr. Berg left Tom's side and advanced to where Mr. Swift was standing.
Together the two emerged from the now fast darkening shop and went
toward the house.

"Who is he?" asked Mr. Sharp of the young inventor in a whisper.

"I don't know," replied the lad; "but, whoever he is, dad seems afraid
of him. I'm going to keep my eyes open."

Chapter Three

Mr. Berg is Astonished

Following his father and the stranger whom the aged inventor had
addressed as Mr. Berg, Tom and Mr. Sharp entered the house, the lad
having first made sure that Garret Jackson was on guard in the shop
that contained the submarine.

"Now," said Mr. Swif