" was the unexpected answer. "I am sorry. Some of
our Secret Service men unearthed something of a plot against you, and I
presumed you had been told to watch out. If you had, the fire might not
have occurred. There must have been some error in Washington. But let
me tell you now, Tom Swift--be on your guard!"

CHAPTER VIII

A SUSPECTED PLOT

The officer's words were so filled with meaning that Tom started. Ned
Newton, too, showed the effect he felt.

"Do you really mean that?" asked the young inventor, looking around to
make sure his father was not present. On account of Professor Swift's
weak heart, Tom wished to spare him all possible worry.

"I certainly do mean it," insisted Lieutenant Marbury. "And, while I am
rather amazed at the news of the fire, for I did not think the plotters
would be so bold as that, it is in line with what I expected, and what
we suspected in Washington."

"And that was--what?" asked Tom.

"The existence of a well-laid plot, not only against our government,
but against you!"

"And why have they singled me out?" Tom demanded.

"I might as well tell it from the beginning," the officer went on. "As
long as you have not received any official warning from Washington you
had better hear the whole story. But are you sure you had no word?"

"Well, now, I won't be so sure," Tom confessed. "I have been working
very hard, the last two days, making some intricate calculations. I
have rather neglected my mail, to tell you the truth.

"And, come to think of it, there were several letters received with the
Washington postmark. But, I supposed they had to do with some of my
patents, and I only casually glanced over them. There was one letter,
though, that I couldn't make head or tail of."

"Ha! That was it!" cried the lieutenant. "It was the warning in cipher
or code. I didn't think they would neglect to send it to you."

"But what good would it do me if I couldn't read it?" asked Tom.

"You must also have received a method of deciphering the message," the
officer said. "Probably you overlooked that. The Secret Service men
sent you the warning in code, so it would not be found out by the
plotters, and, to make sure you could understand it, a method of
translating the cipher was sent in a separate envelope. It is too bad
you missed it."

"Yes, for I might have been on my guard," agreed Tom. "The red shed
might not have burned, but, as it was, only slight damage was done."

"Owing