He might deposit the precious stone in any place especially guarded and set apart--like a banker's or jeweller's strong-room--for the safe custody of valuables of high price.

His main personal responsibility in the matter was to be of the passive kind.

He was to undertake either by himself, or by a trustworthy representative--to receive at a prearranged address, on certain prearranged days in every year, a note from the Colonel, simply stating the fact that he was a living man at that date.

In the event of the date passing over without the note being received, the Colonel's silence might be taken as a sure token of the Colonel's death by murder.
In that case, and in no other, certain sealed instructions relating to the disposal of the Diamond, and deposited with it, were to be opened, and followed implicitly.

If my father chose to accept this strange charge, the Colonel's papers were at his disposal in return.