bolts of the back garden gate. Five minutes later Knopf
was in the house, in a hot bath, getting rid of the disguise of our
friend the tramp. Remember that again here the detective did not
actually see him.

"The next morning Mr. Knopf, black hair and beard and all, was himself
again. The whole trick lay in one simple art, which those two cunning
rascals knew to absolute perfection, the art of impersonating one
another.

"They are brothers, presumably--twin brothers, I should say."

"But Mr. Knopf--" suggested Polly.

"Well, look in the Trades' Directory; you will see F. Knopf & Co.,
diamond merchants, of some City address. Ask about the firm among the
trade; you will hear that it is firmly established on a sound financial
basis. He! he! he! and it deserves to be," added the man in the corner,
as, calling for the waitress, he received his ticket, and taking up his
shabby hat, took himself and his bit of string rapidly out of the room.

CHAPTER VII

THE YORK MYSTERY

The man in the corner looked quite cheerful that morning; he had had two
glasses of milk and had even gone to the extravagance of an extra
cheese-cake. Polly knew that he was itching to talk police and murders,
for he cast furtive glances at her from time to time, produced a bit of
string, tied and untied it into scores of complicated knots, and
finally, bringing out his pocket-book, he placed two or three
photographs before her.

"Do you know who that is?" he asked, pointing to one of these.

The girl looked at the face on the picture. It was that of a woman, not
exactly pretty, but very gentle and childlike, with a strange pathetic
look in the large eyes which was wonderfully appealing.

"That was Lady Arthur Skelmerton," he said, and in a flash there flitted
before Polly's mind the weird and tragic history which had broken this
loving woman's heart. Lady Arthur Skelmerton! That name recalled one of
the most bewildering, most mysterious passages in the annals of
undiscovered crimes.

"Yes. It was sad, wasn't it?" he commented, in answer to Polly's
thoughts. "Another case which but for idiotic blunders on the part of
the police must have stood clear as daylight before the public and
satisfied general anxiety. Would you object to my recapitulating its
preliminary details?"

She said nothing, so he continued without waiting further for a reply.

"It all occurred during the York racing week, a time which brings to the
quiet cathedral c