Donald explained in as few words as possible.

The conductor signalled the guards to him and told them what
Donald had said.

"What had we better do?" asked the conductor.

"We had better go back to Pachuca for help," replied the guards.

"And let the Zapatistas escape!" exclaimed Billie hotly. "What do
you want to do that for?"

"We have only six guards," the conductor explained, "and----"

"And that, with us, makes ten," interrupted Billie.

The conductor regarded the boy with surprise.

"Do you mean you will join us to help capture the bandits?"

"What do you think we're here for?" asked Billie.

"Yes," chimed in Adrian. "What do you suppose we stopped the
train for?"

"But even ten are no match for twenty or more," declared the
guard.

"Of course they are," said Donald, "if the twenty are taken by
surprise."

"Which they will not be if we don't act pretty quick," insisted
Billie. "Come on! Let's go after them," and he climbed up onto
the car.

"That's what I say," said Pedro, following Billie's example.

Without more words the others followed and the conductor gave the
signal to go ahead.

"How about the horses?" asked Donald, turning to Pedro.

"They'll be all right; but if we capture the Zapatistas we'll
have horses enough any way."

"And if we don't," remarked Billie grimly, "there'll be some
riderless horses any way."

"Let us hope that they will not be the ones we have left behind,"
said Donald gravely.

CHAPTER II.

A STRANGE MIX-UP.

While the train was gathering headway the conductor and the
guards rounded up all the men they could find on the train who
were armed. There were more than a dozen, so that in point of
numbers, the force on the train nearly equalled the Zapatistas.
These were so stationed at the windows that they could give the
would-be robbers a warm reception.

"We must use some strategy," declared Adrian, "or we will simply
succeed in killing a few and scaring away the others. That will
not be a very brilliant deed."

"No," from Donald, "but it will save the bullion. What's your
plan?"

"Well, I was thinking it would be a good plan to separate the
train."

"How?"

"You can see it is all down grade from here to where the bandits
are waiting for us."

"Yes."

"As soon as we get to running a good speed, Billie and I will go
into the express car with the three guards. You and Pedro stay
here with the other guards and the passengers. As we near t