tative of Calomares, the Mexican landowner who is
backing the northern rebels, sought him out with a proposition that he
betray his employers. The rebels, as I suspected, wanted to make
trouble for President Obregon, of Mexico, by embroiling him with the
United States. And the way they wanted to set about it was by raiding
the independent oil operators. They needed a spy at our headquarters,
and they proposed that Rollins should become their man.

"Then Rollins had an inspiration. He told the Mexicans that if they
would help him, he would aid them. It was agreed. The agent who had
acted for Calomares in the negotiations was this German, Von Arnheim,
an aviator and a German secret agent in Mexico during the war. He took
the man Morales with him to Mr. Hampton's Long Island home to steal
the duplicate list of independent leases and other data which Rollins
had learned was kept there."

"That's where I came in," grinned Bob.

"Yes," said his father, "and it was because you foiled them that
Rollins came into possession of Mr. Hampton's own original copy of the
list and other data. For he stole it from Mr. Hampton's effects after
Von Arnheim and Morales had carried him away captive in our airplane."

"How about this attack on us yesterday?" asked Jack.

"As you suspected, it was for the purpose of capturing me, too," said
Mr. Temple. "And Rollins had let the bandits know when I would arrive.
Remedios was his go-between."

"Well," said Jack, "there's only one thing more."

"What is that?" asked Frank.

"Why, I'd like to know whom Rollins radioed to last night."

"I found that out, too," said Mr. Temple. "He was talking to the
Calomares ranch in Old Mexico, which has a very powerful station,
according to Rollins. He says the German, Von Arnheim, told him that
there are similar powerful radio stations scattered throughout Mexico
and South America, all built by German money for the use of its spy
system. And he said this German told him the most powerful station of
all was on an island in the Caribbean, and that it was so powerful it
could communicate with Nauen, Germany."

It was apparent that Mr. Temple had concluded his explanation, and Bob
and Frank began to ply him with questions. Jack, however, stood
silent, his face averted. Mr. Temple presently broke from the others
and laying a hand on Jack's shoulder whirled him about.

"Father?" asked he, in a kindly tone.

"Yes, sir."

"Well, Jack, I've got the beginn