llyn John, previous to being
appointed to Department Z., Malcolm Sage had bluntly criticised the
Government's methods of dealing with the spy peril.

"You're all wrong, sir," he had said. "If you spot a spy, you arrest,
imprison or deport him, according to the degree of his guilt. Any fool
could do that," he had added quietly.

"And what would you do, Sage?" inquired Mr. Llewellyn John, who never
took offence at the expression of any man's honest opinion, no matter
how emphatically worded.

"I should watch him," was the laconic reply. "Just as was done before
the war. You didn't arrest spies then, you just let them think they
were safe."

For a few moments Mr. Llewellyn John had pondered the remark, and then
asked for an explanation.

"If you arrest, shoot or intern a spy, another generally springs up in
his place, and you have to start afresh to find him; he may do a lot of
mischief before that comes about." Sage gazed meditatively at his
finger-nails, a habit of his. "On the other hand," he continued, "if
you know your man, you can watch him and generally find out what he's
after. Better a known than an unknown danger," he had added oracularly.

"I'm afraid they wouldn't endorse that doctrine at Scotland Yard,"
smiled Mr. Llewellyn John.

"Scotland Yard is a place of promoted policemen," replied Sage,
"regulation intellects in regulation boots."

Mr. Llewellyn John smiled. He always appreciated a phrase. "Then you
would not arrest a burglar, but watch him," he said, glancing keenly at
Sage.

"The cases are entirely different, sir," was the reply; "a burglar
invariably works on his own, a spy is more frequently than not a cog of
a machine and must be replaced. He seldom works entirely alone."

"Go on," Mr. Llewellyn John had said, seeing that Sage paused and was
intently regarding his finger-nails of his right hand.

"Even when burglars work in gangs, there is no superior organisation to
replace destroyed units," continued Sage. "With international secret
service it is different; its casualties are made good as promptly as
with a field army."

"I believe you're right," said Mr. Llewellyn John. "If you can
convince Colonel Walton, then Department Z. can be run on those lines."

Malcolm Sage had found no difficulty in convincing his chief, a man of
quiet demeanour, but unprejudiced mind. The result had been that
Department Z. had not so far caused a single arrest, although it had
countered m