t to assist me?"_ another letter
ran. It was likewise type-written, and from the same source.
_"Recollect you did so once, and were well paid for it. You
had enough to keep you in luxury for years had you not so
foolishly frittered it away on your so-called friends. Any
of the latter would give you away to the police to-morrow
for a five-pound note. This, however, is my last appeal to
you. If you help me I shall give you one hundred pounds,
which is not bad payment for an hour's work. If you do not,
then you will not hear from me again.--Z."_

"Seems a bit brief, and to the point," was the elder constable's
remark. "I wonder what is the affair mentioned by this mysterious
correspondent? Evidently the fellow intended to bring off a robbery,
or something, and Lane refused to give his aid."

"Apparently so," replied Ambler, fingering the last letter remaining
in his hand. "But this communication is even of greater interest," he
added, turning to me and showing me writing in a well-known hand.

"I know that writing!" I cried. "Why--that letter is from poor Mrs.
Courtenay!"

"It is," he said, quietly. "Did I not tell you that we were on the eve
of a discovery, and that the dead man lying there could have told us
the truth?"

CHAPTER XXIX.

THE POLICE ARE AT FAULT.

Ambler Jevons read the letter, then handed it to me without comment.

It was written upon the note-paper I knew so well, stamped with the
neat address "Neneford," in black, but bearing no date. What I read
was as follows:--

_"Sir,--I fail to comprehend the meaning of your words when
you followed me into the train at Huntingdon last night. I
am in no fear of any catastrophe; therefore I can only take
your offer of assistance as an attempt to obtain money from
me. If you presume to address me again I shall have no other
course than to acquaint the police._

"_Yours truly_

"MARY COURTENAY."

"Ah!" I exclaimed. "Then he warned her, and she misunderstood his
intention."

"Without a doubt," said Ambler, taking the letter from my hand. "This
was written probably only a few days before her death. That man," and
he glanced at the prostrate body, "was the only one who could give us
the clue by which to unravel the mystery."

But the dead man's lips had closed, and his secret was held for ever.
Only those letters remained to co