n Tarling called, and the sergeant on duty in the
little office by the main door hurried forward.

"This came for you two hours ago, sir," he said "We thought you were in
Hertford."

"This" was a letter addressed in pencil, and Mr. Milburgh had made no
attempt to disguise his handwriting. Tarling tore open the envelope and
read the contents:

"Dear Mr. Tarling," it began. "I have just read in the _Evening
Press_, with the deepest sorrow and despair, the news that my dearly
Beloved wife, Catherine Rider, has been foully murdered. How
terrible to think that a few hours ago I was conversing with her
assassin, as I believe Sam Stay to be, and had inadvertently given
him information as to where Miss Rider was to be found! I beg of you
that you will lose no time in saving her from the hands of this
cruel madman, who seems to have only one idea, and that to avenge
the death of the late Mr. Thornton Lyne. When this reaches you I
shall be beyond the power of human vengeance, for I have determined
to end a life which has held so much sorrow and disappointment.--M."

He was satisfied that Mr. Milburgh would not commit suicide, and the
information was superfluous that Sam Stay had murdered Mrs. Rider. It
was the knowledge that this vengeful lunatic knew where Odette Rider was
staying which made Tarling sweat.

"Where is Mr. Whiteside?" he asked.

"He has gone to Cambours Restaurant to meet somebody, sir," said the
sergeant.

The somebody was one of Milburgh's satellites at Lyne's Store. Tarling
must see him without delay. The inspector had control of all the official
arrangements connected with the case, and it would be necessary to
consult him before he could place detectives to watch the nursing home
in Cavendish Place.

He found a cab and drove to Cambours, which was in Soho, and was
fortunate enough to discover Whiteside in the act of leaving.

"I didn't get much from that fellow," Whiteside began, when Tarling
handed him the letter.

The Scotland Yard man read it through without comment and handed it back.

"Of course he hasn't committed suicide. It's the last thing in the
world that men of the Milburgh type ever think about seriously. He is a
cold-blooded villain. Imagine him sitting down to write calmly about his
wife's murderer!"

"What do you think of the other matter--the threat against Odette?"

Whiteside nodded.

"There may be something in it," he