The samples of gold are handed over at the docks to some
accredited representative of the firm--generally either Mr. Reuben or
Mr. Walter--who has been despatched to meet the ship, and conveyed
either to the bank or to the works according to circumstances. Of course
every effort is made to have as little gold as possible on the premises,
and the bars are always removed to the bank at the earliest opportunity;
but it happens unavoidably that samples of considerable value have often
to remain on the premises all night, and so the works are furnished with
a large and powerful safe or strong room for their reception. This safe
is situated in the private office under the eye of the principal, and,
as an additional precaution, the caretaker, who acts as night-watchman,
occupies a room directly over the office, and patrols the building
periodically through the night.

"Now a very strange thing has occurred with regard to this safe. It
happens that one of Mr. Hornby's customers in South Africa is interested
in a diamond mine, and, although transactions in precious stones form no
part of the business of the house, he has, from time to time, sent
parcels of rough diamonds addressed to Mr. Hornby, to be either
deposited in the bank or handed on to the diamond brokers.

"A fortnight ago Mr. Hornby was advised that a parcel of stones had been
despatched by the _Elmina Castle_, and it appeared that the parcel was
an unusually large one and contained stones of exceptional size and
value. Under these circumstances Mr. Reuben was sent down to the docks
at an early hour in the hope the ship might arrive in time for the
stones to be lodged in the bank at once. Unfortunately, however, this
was not the case, and the diamonds had to be taken to the works and
locked up in the safe."

"Who placed them in the safe?" asked Thorndyke.

"Mr. Hornby himself, to whom Mr. Reuben delivered up the package on his
return from the docks."

"Yes," said Thorndyke, "and what happened next?"

"Well, on the following morning, when the safe was opened, the diamonds
had disappeared."

"Had the place been broken into?" asked Thorndyke.

"No. The place was all locked up as usual, and the caretaker, who had
made his accustomed rounds, had heard nothing, and the safe was,
outwardly, quite undisturbed. It had evidently been opened with keys and
locked again after the stones were removed."

"And in whose custody were the keys of the safe?" inquired Thornd