The speaker sprang to the ground and disappeared around the corner of the shed with the words.

His companion, who had been stooping on one knee in his prying operations, essayed to join him, slipped, tilted over, and before he could recover himself Bart was upon him.

“What are you about here?” demanded the latter.

The prisoner was of man-like build and proportions.  He did not speak, and tried to keep his features hidden from the rays of the near switch light.

“Lemme go!” he mouthed, with purposely subdued intonation.

“Not till I know who you are—­not till I find out what you’re up to,” declared Bart.  “Turn around here.  I’ll stick closer than a brother till I see that face of yours!”

He swung his captive towards the light, but a broad-peaked cap and the partial disguise of a crudely blackened face defeated his purpose.

Bart was about to shout to his father in front, or to his roustabout friend, whom he expected must be somewhere near by this time, when his captive gave a jerk, tore one arm free, and whirled the other aloft.

His hand clenched the implement he had used to pry away the bars, and Bart now saw what it was.

The object the mysterious robber was utilizing for burglarious purposes, was the signal flag used at the switch shanty where Lem Wacker had been doing substitute duty that day.

It consisted of a three foot iron rod, sharpened at the end.  At the blunt end the strip of red flag was wound, near the sharp end the conventional track torpedo was held in place by its tin strap.

“Lemme go”; again growled the man.

“Never!” declared Bart.

The man’s left arm was free, and he swung the iron rod aloft.  Bart saw it descending, aimed straight for his head.  If he held on to the man he could scarcely evade it.

He let go his grip, ducked, made a pass to grasp the burglar’s ankle, but missed it.

An explosion, a sharp flare, a keen shock filled the air, and before Bart could grip the man afresh he had sprung from the platform and vanished.

At the same instant the flag rod clattered to the boards, and a second later, rubbing his face free from sudden pricking grains of powder, Bart saw what had happened.

The blow intended for him had landed upon one of the iron bars of the window with a force that exploded the track torpedo.

It had flared out one broad spiteful breath, sending a shower of sparks among the big mass of fireworks in the storage room, and amid a thousand hissing, snapping explosions the express shed was in flames.

CHAPTER IV

BLIND FOR LIFE

Bart’s first thought was of his father.  He instantly leaped from the platform.

As he did so there was a violent explosion in the storage room, the sashes were blown from place outright, and Bart dodged to escape a shower of glass.