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 like the other there must be five rows of thirteen letters each, or thirteen rows of five each. I'll try the five rows first. That's more like the other cipher."