"And you think spies set this fire?"
"I certainly do."
"But what measures shall I adopt against this plot?" Tom asked.
"We will talk that over," said Lieutenant Marbury. "But, before I go into details, I want to give you another warning. You must be very careful about—"
A sudden knock on the door interrupted the speaker.
CHAPTER IX
THE RECOIL CHECK
"Who is that?" asked Ned Newton, with a quick glance at his chum.
"I don't know," Tom answered. "I left orders we weren't to be disturbed unless it was something important."