t unknown, resident in the city of London."

"That's very important," said the Queen. "Anything more?"

"No," he said, "that's all I've got."

The Queen handed over the diary. It was Phillips' turn to write.

"I observed," she said, "that the envelope is of the kind used by
business men, an office envelope; also that the stamp is put on
crooked."

Phillips looked at the stamp. It was put on crooked.

"From this I infer," said the Queen, "either that the man in
London----What did you call him?"

"Person at present unknown," said Phillips.

"Either that the person at present unknown was (a) habitually careless
about details, or that (b) though usually careful he was in a hurry
when he despatched this letter."

"By Jove!" said Phillips, "but, I say, mightn't somebody else, an
office boy or some one, have put on the stamp?"

"Not on a letter of this kind," said the Queen. "The writer wouldn't
have trusted any one else."

"It's frightfully clever of you," said Phillips, "to have thought of
all that."

"It does not lead to anything very definite yet," said the Queen. "But
you'll find it will all fit together--like a jigsaw puzzle you
know--when we get to work on the other two clues. We can't expect to
solve a mystery of this sort straight off. We've only been at it two
hours."

Kalliope stood all the time at the far end of the balcony watching the
Queen. She knew nothing about the investigation of the island mystery
which was going on under her eyes. But she was a young woman who had
lived a simple and natural life. In some things she was far wiser than
her mistress. She seems to have realized that the Queen and Phillips
were making, without knowing it, considerable progress into the heart
of another, much more enthralling, mystery. As a chaperone Kalliope
was negligible.

"The next clue," said the Queen, "is Smith. We must shadow him."

"Day and night," said Phillips.

"And Stephanos. Stephanos was with him when he went to the cavern that
morning."

"Stephanos is in it up to the neck," said Phillips. They shadowed
Smith for the rest of that day. They stole on tip-toe about the house
and burst suddenly into rooms where Smith was at work, coming upon him
unexpectedly. They hid in cupboards and behind curtains in rooms which
Smith was likely to enter. They left letters, written in cipher, and
marked coins in prominent places where Smith could hardly fail to see
them. Kalliope conceived that an elaborate g