His peace of mind was not increased by the reflection that had he
waited and continued to shadow Fairfield he might have discovered the
whereabouts of the missing diplomat. Now he had merely given notice as
plainly as though he had shouted from the housetops that Fairfield was
under observation. He had committed a blunder, and he did not forgive
blunders easily, especially in himself.

Even a bath and a change into his normal clothing did not restore his
equanimity. In his office he found Green, with a strange excitement in
his usually stolid face.

"Hello, Mr. Green. What's wrong?" he demanded.

The veteran chief detective-inspector pulled at his moustache.

"I don't know, sir, yet. You've come just in time. Waverley is missing.

"Waverley missing! That's nonsense. He was put on to relieve Norman in
shadowing Ivan Abramovitch."

"He's missing," repeated the other doggedly. "Ivan went into a shop with
an entrance in two streets, and the man who was assisting Waverley
slipped round to the other side. He waited there an hour, and then went
to look for Waverley."

The superintendent gave a short, contemptuous laugh.

"Green, I guess you've been working too hard lately. You ought to apply
for a fortnight's leave. Can't you see, Ivan came out and that Waverley
never had time to give the tip to his man, but followed him straight
away? There ought to have been three men on the job."

Green drew himself up stiffly. Foyle had not recovered from the
irritation caused by his own mistake, otherwise he would not have spoken
as he did. Green was not the kind of man to hastily jump to conclusions.

"A third was not available when Waverley left," he said. "Here is why I
say Waverley is missing. It came by messenger five minutes ago,
addressed to you. As senior officer I opened it."

Foyle took a typewritten sheet of paper from the other's hand. It read
simply--

"DEAR MR. FOYLE,--You had better call your men off. We have got one
of them safe, and hold him as a hostage for our own safety. If your
people go on trying to make things unpleasant for us, things will
get unpleasant for him. This is not melodrama, but brutal fact."

There was no signature. Foyle's square jaw became set and grim. He had
no doubt that the unknown writer fully meant the threat. He liked
Waverley, yet the thought of the other's peril did not sway him for a
moment. The man had fallen a victim to one of the risks of his
profession.