were away in Swanage during the first week of November?" I
asked very seriously.

"Yes, we went down on the last day of October, and we were back here
in the middle of November. My wife's sister was very ill, and her
husband didn't expect her to live. So I remember the dates only too
well."

"Then the family were in town on the date I mention."

He considered a moment.

"Oh! Of course they were. They must have been."

I glanced again around the room, full of amazement and wonder.

The man's failure to give me any details regarding the extremely
attractive girl who had died upon his mistress's bed held me gripped
in uncertainty. The mystery was even more puzzling now that I had
started to investigate.

As I stood in that room a thousand strange reflections flashed across
my mind.

Why had I, a mere passer-by, been called in so suddenly to be taken
into the intimacy of the millionaire's household? Was it by mere
accident that I had been invited in, or was it by careful design? I
had lost five thousand pounds by foolish speculation, and yet I had
regained it by being party to a criminal offence.

Again, who was the pretty, dark-haired girl who had first uttered
those hysterical screams, and then, while fully dressed, had died upon
Mrs. De Gex's bed? Further, if the mysterious dead girl had been niece
of the millionaire surely my friend the caretaker would have known
her?

I confess that I now became more bewildered than ever.

That a girl named Gabrielle Engledue--whoever she might have been--had
died, and that I had forged a certificate showing the cause of death
were hard, solid facts. But the mystery of it all was complete.

That I had been the victim of some very carefully prepared and subtle
plot was apparent, and it had become my own affair to investigate it
and bring to justice those who were responsible for the poor girl's
death.

Time after time I questioned the caretaker regarding the existence of
the millionaire's niece, Miss Engledue, but it was plain to me that he
had no knowledge of any such person.

"Was there not a death in this house--about five weeks ago?" I asked.

"Death?" he echoed. "Why, no, sir. You must be dreaming. If there had
been a death while I was away, either my wife or I would certainly
have heard about it." And he looked suspiciously at me as though he
believed I had taken leave of my senses.

An hour later I was back at Rivermead Mansions, where Harry, for whom
I had