In another minute the men would open the wagon doors, pull him out, perhaps assault him, take the registered mail and fly.

Andy had only a second to act in.  He theorized that the wagon, following the alley, was now probably halted in some secluded side lane.

To escape the clutches of the would-be robbers was everything.  Andy, having no weapon of defence, was no match for them.

“If the rig once reaches the crowded streets, I’m safe,” thought Andy.

Then he carried out a speedy programme.  Forming his lips in a pucker, as he had seen Ripley do, Andy uttered two sharp whistles, then a clear, resounding hiss.

“Thunder!” yelled a voice outside.

“Ouch!” echoed a second.

The horse had given one wild, prodigious bound at hearing the familiar signal.

The vehicle must have grazed one of the thieves.  Its front wheels knocked the other down.

“My!  I’m in for it,” instantly decided Andy.

For, swayed from side to side, he realized that the circus wagon was dashing forward at runaway speed.

CHAPTER XVII

A WILD JOURNEY

Andy Wildwood found himself in a box, in more ways than one.

Judging from the sounds he had heard, the men bent on securing the registered mail pouch had been baffled.  The old circus horse had started on a sudden and surprisingly swift sprint.  From the feeling of turns, jerks and swings, Andy decided that within four minutes the rig had left the post-office fully half-a-mile to the rear.

“I’ve started the horse all right,” said Andy.  “Old Ripley’s signal has acted like a charm.  How to stop the animal, though.  That is the present question?”

Andy ran at the two rear doors of the wagon.  He steadied himself, arms extended so as to touch either side of the box.  Then he gave the doors a tremendous kick with the sole of his shoe.

The doors did not budge.  He felt over their inner surfaces where they came together.  The lock was set in the wood.  They could be opened only from the outside.

The wagon box had one aperture, Andy discovered.  This was a small ventilating grating up in one corner above the seat.

He sprang up on the newspaper bag.  This brought his eyes on a level with the grating.  It was about four by six inches, with slanting slats.  Andy could see down at the horse and ahead along the road.

He grew excited and somewhat uneasy as he looked out.  Lute was a sight for a race track.  Her head down, mane flowing, tail extended, she was covering the ground with tremendous strides.

Farther back on the route Andy had felt the wagon collide with curbs and with other vehicles.  Once there was a crash and a yell, and he felt sure they had taken a wheel off a rig they passed.  Now, however, they appeared to be quite clear of the town proper.