this made him careless does not matter, but the fact was that he
left Bower more to himself, and alone in the experimental shop
several times.

And it was on one of these occasions, when Tom had been for
some time in one of the other shops, where he and Jackson were in
consultation over a new machine, that as he came back to the test
room unexpectedly, he saw Bower move hastily away from in front
of the safe. Moreover, Tom was almost certain he had heard the
steel door clang shut as he approached the building.

And then, before he could ask his helper a question, Tom looked
from a window and saw a stranger running hastily along the side
of the building where his trial motor was being set up.

"Who's that? Who is that man? Did he come in here? Was he
tampering with my safe?" cried Tom. He saw Bower hesitate and
change color, and Tom knew it was time to act.

The window was open, and with one bound the young inventor was
out and running after the stranger he had seen departing in such
a hurry. The man was but a short distance ahead of him, and Tom
saw he was stuffing some papers into his pocket.

"Here! Come back! Stop!" ordered Tom, but the man ran on the
faster.

"That's a spy as sure as guns!" reflected Tom Swift. "And Bower
is in with him!" he added. "I've got to catch that fellow!" and
he speeded his pace as he ran after the fellow.