Just here a slight incident interrupted the lad's thoughts so suddenly
that he sprang to his feet--unconsciously his eyes had been fixed on the
bell-cord that ran through the entire train to the cab of the locomotive.
It had hung a little slack, but all at once this slack was jerked up as
though some one had pulled the cord. This would have been a signal to stop
the train, and if the train were to be stopped at that point something
must be wrong. A backward glance showed Conductor Tobin and the other
brakeman to be still quietly engaged in conversation. Neither of them
could have pulled the cord. Rod stepped to the door and looked out. The
train was tearing along at a terrific speed, and the rush of air nearly
took away his breath. There was no sign of slackening speed and everything
appeared to be all right. The next car ahead of the coach was the money
car. At least Conductor Tobin had thought so, though none of the trainmen
was ever quite sure which one of the half dozen or more express cars it
was. Its rear door was of course closed and locked, but some impulse moved
Rod to clamber up on its platform railing and peer through the little hole
by which the bell-cord entered. He could not see much, but that which
was disclosed in a single glimpse almost caused his heart to cease its
beating. Within his range of vision came the heads of two men evidently
engaged in a struggle and one of them wore a mask over the lower part of
his face. The next instant Rod had sprung down from his perilous perch and
dashed back into the coach shouting breathlessly:

"There's a masked man fighting the messenger in the money car!"

CHAPTER XXI.

OVER THE TOP OF THE TRAIN.

At Rodman's startling announcement Conductor Tobin sprang to his feet,
reached for the bell-cord, and gave it two sharp pulls. A single whistle
blast from the locomotive made instant reply that his signal was received
and understood. So promptly was it obeyed that as the conductor and his
two brakemen ran to the front platform to swing far out and look along the
sides of the express cars ahead of them, the grinding brakes were already
reducing the speed of the flying train.

Suddenly a pistol shot rang angrily out, and a bullet crashed into the
woodwork close above Rod Blake's head. He and the conductor were leaning
out on one side while the other brakeman occupied the opposite one.

"Give the signal to go ahead at once, or I'll come back there and blow
y