sages by
motor-car, and probably sent code letters through the mails. For all
ordinary correspondence they used these slower, safer methods. Only
when they absolutely had to, did they employ the wireless. So we must
assume that they had to now."

He paused and glanced from face to face. "But why the change of
cipher?" he continued. "It must be because they fear that the old
cipher will be understood."

Again the captain fell silent. "What can have happened?" he inquired
soberly, "that makes the use of wireless so imperative? What can it
be? Only something new and unforeseen. And what could there be new
and unforeseen except the detection of their plot? More and more I am
convinced that these plotters have been alarmed."

He fell into a brown study for a moment. "This message can mean
nothing else," he said after a little. "It is imperative that we learn
what it is at the earliest possible moment. Make four copies of the
message you took, Henry."

Captain Hardy's first lieutenant took the paper from his leader's hand
and on four sheets of paper copied the string of letters he had picked
from the air.

"Now, boys," said the leader of the patrol, when the copies were
complete, "put your thinking caps on. Each of you take one of these
copies and see what you can make of it. You know how we deciphered the
other cipher."

In another moment four boys were wrinkling their foreheads as they bent
over the cryptic strings of letters. And over the room came a hush
deep as midnight's.

For a few moments nobody broke the silence. Each boy was busy with his
own thoughts.

Henry was scowling at his paper. Willie was studying the letters
before him, as in earlier days he had studied the landscapes about Camp
Brady and the Elk City reservoir. Lew already had a hopeless look on
his face. At threading the forest he was second to none in skill; but
at untangling mental puzzles, he had small ability. The nimble-witted
Roy was already setting about his task with that keenness so
characteristic of him.

"Sixty-five letters," he said to himself. "If this cipher is anything
like the other, those letters must be arranged in columns of equal
size."

For a second he sat scanning the letters. Then he muttered, "What will
divide sixty-five evenly?" And a moment later, he answered his own
query by adding, "Five, and thirteen."

He paused and again ran his eye along the row of letters. "If this
cipher works lik