d it come from?" he asked in a shrill, querulous tone.
"Who brought back my secret casket?"

"Yours?" came from every one in the room.

"Yes! Mine! Mine!!" he almost screamed.

"He's raving!" cried Josie. "Can't some one do something for
him?"

"No," he replied, and his voice became more calm, "I am not
raving. I know whereof I speak. Quick! Let me look within it to
see that all is safe."

"It is locked, Father," said Lucia, coming to his side, "and we
have no key."

"I can unlock it," he cried. "I can unlock it. Give it to me.
Give it to me."

He staggered forward and seized the box in his hands. For several
seconds he fumbled with it, turning it first upon one side and
then upon another, and at last raised the lid. He thrust in his
hand and then stopped as one stupefied.

"Empty! Empty!" he gasped in an almost audible whisper. "The plan
of Montezuma's mine is gone! Gone!!"

A moment he stood and gazed around upon the faces of those in the
room and then collapsed upon the floor.

Quickly the boys picked him up and carried him to his bed and the
attending physician was summoned.

Billie picked up the box and examined it curiously.

"I wonder how he opened it?" he mused. "There must be some sort
of a spring somewhere."

He felt the box all over, but could find nothing. Then he closed
it and set it upon the table. A moment later Donald picked it up
and tried to open it, but it was locked fast.

"Nothing but mysteries," he said. "I'm getting tired of them. But
before anything else happens, I'm going around and notify Don
Esteban that the box is here."

"I'll go with you," said Adrian.

"No, you'd better stay here. I'll take a mozo with me."

He ran hastily down the stairs and a minute later the boys heard
the gate close behind him.

"I guess this is the quickest way," thought Donald as he gained
the sidewalk. "I'll not bother with a mozo. With American
soldiers on guard and my automatic in my pocket, I have nothing
to fear."

A couple of minutes later he was ringing the bell at Don
Esteban's house. He was hastily admitted and at once conducted to
that gentleman's presence, where he narrated hastily what had
occurred at the other house.

"Who is this old man?" Don Esteban asked of Donald.

Donald explained as best he could.

"Which is mighty little," he declared when he had finished. "He
is the greatest mystery we have ever encountered. There is no
doubt that he is an Indian, but he speaks E