stic.

He put the flowers aside and picked up the envelope, looked it over
carefully, then, with a peculiarly thin and very sharp knife, he cut the
sealing of the flap so neatly that it could be resealed and no one
suspect it had been opened. As he turned back the flap, a small
unmounted photograph fell out and lay face upward on the table.

Harleston gave a low whistle of surprise.

It was Madeline Spencer.

II

THE VOICE ON THE WIRE

"Good morning, madame!" said Harleston, bowing to the photograph. "This
is quite a surprise. You're taken very recently, and you're worth
looking at for divers aesthetic reasons--none of which, however, is the
reason for your being in the envelope."

He drew out the sheet of paper and opened it. On it were typewritten,
without address nor signature, these letters:

DPNFNZQFEFBPOYVOAEELEHHEJYD
BIWFTCCFVDXNQYCECLUGSUGDZYJ
ENRYUIGYBSNRTDUHJWHGYZIPEPA
WPPOIMCHEIPRFBJXFVWWFTZNJPY
UFJDILDCEMBRVZDAYVAWALUMOFN
FCVDPGLPWFUUWVIEPTKVIPUMSFZ
NPSJJRFYASGZSDACSIGYUOFCEXA
AOIDJJFCJPSONPKUUYVCVCTIHDP
XMNOYKENHUSKHYMSFRRPCYWSLLW
SMVPPUNEIFIDJLZRWEHPQGODFUZ
TCEMQIQWNFYJTAALUMHJXILEEHY
ISOVOAZUCUDINBRLUZICUOTTUSV
LPNFFVQFANPVCYJHILTPFISGHCW
HYICPPNFDOUOCLDUWEIVIPJNQBV
ZLMIJRVKDSFRLWEGBKQYWSFFBEI
YORHMYSHTECPUTMPJXFNRNEEUME
ILJBWV.

"Cipher!" commented Harleston, looking at it with half-closed eyes....
"The Blocked-Out Square, I imagine. No earthly use in trying to dig it
out without the key-word; and the key-word--" he gave a shrug. "I'll let
Carpenter try his hand on it; it's too much for me."

He knew from experience the futility of attempting the solution of a
cipher by any but an expert; and even with an expert it was rarely
successful.

As a general rule, the key to a secret cipher is discovered only by
accident or by betrayal. There are hundreds of secret ciphers--any
person can devise one--in everyday use by the various departments of the
various governments; but, in the main, they are amplifications or
variations of some half-dozen that have become generally accepted as
susceptible of the quickest and simplest translation with the key, and
the most puzzling without the key. Of these, the Blocked-Out Square,
first used by Blaise de Vigenerie in 1589, is probably still the most
generally employed, and, because of its very simplicity, the most
impossible of solution. Change the key-word and one has a new cipher.
Any word will do; nor doe