"Ready for the next tussle with cryptography?" Crossle smilingly greeted his young nephew the following evening.
"I've got a neat little problem to test your ingenuity. The story is quite simple. During the early part of 1918, there were a series of robberies in Washington that, for the time, completely baffled the police. They always involved the looting of safes in office buildings without the use of any tools or explosives, so that it looked as though the crook was another Jimmy Valentine or Houdini. The underlying similarity of the jobs identified them as the work of one mind. Suspicion was strongly directed to a notorious cracksman known as 'Silky Pete' who'd been recently released from a two-year stretch in Atlanta. But without a shred of proof the police were unable to arrest him. Finally, after a job that involved the loss of several hundred dollars worth of negotiable securities, the police decided to get 'Silky' and 'sweat' him. He was located in New York City and jailed. During the first night he was observed to pass a slip of paper to a prisoner in an adjacent cell who was being held on a minor charge and who would be released the next morning."
"The slip bore the following cipher message:"
CCPPM KVNDP CQHYJ JAPDQ PAM
"This in another exercise in training your eye in piecing letters together," Crossle added. "It's a knack which comes, as a rule, only with repeated practice and is absolutely indispensable to success in cryptography. Let's see what luck you have."