"Well, it is on the same principle as the safe deposit boxes in a bank.
The depositor has one key, and the bank the other. The box cannot be
opened by either party alone. Both keys must be used. That insures
that no one person alone can get into the box. It was the same way with
this safe. The combination was in two parts."

"And did my father set it that way?"

"He must have done so, or had some one arrange the combination for him."

"Then he - he must have shared the combination with some one else!" There
was fright in Viola's eyes, and a catch in her voice.

"Yes," assented the expert. "Either that or he set it that way merely
for what we might call a 'bluff,' to throw any casual intruder off the
track. Your father might have possessed both combinations himself."

"And yet he might have shared them with - with another person?"

"Yes."

"And the other-the other person" - Viola hesitated noticeably over the
word - "would have to be present when the safe was opened?" She did not
say "he" or "she."

"Well, not necessarily," answered the expert. "He might have had the
combination in two parts, and used both of them himself. It is often
done. Though, of course, he could, at any time, have shared the secret
of the safe with some one else."