Quest had stolen a yard or two nearer during this brief colloquy.  Gallagher’s mate from behind shouted out a warning just a second too late.  With a sudden kick, Quest sent the revolver flying across the room, and before the Irishman could recover, he struck him full in the face.  Notwithstanding his huge size and strength, Gallagher reeled.  The operator, who had just begun to realize what was happening, flung himself bodily against the two thugs.  A shot from the tangled mass of struggling limbs whistled past Quest’s head as he sprang to the window which overlooked the track.  The freight had already almost passed.  Quest steadied himself for a supreme effort, crawled out on to the little steel bridge and poised himself for a moment.  The last car was just beneath.  The gap between it and the previous one was slipping by.  He set his teeth and jumped on to the smooth top.  For several seconds he struggled madly to keep his balance.  He felt himself slipping every minute down to the ground which was spinning by.  Then his right heel caught a bare ledge, scarcely an inch high.  It checked his fall.  He set his teeth, carefully stretched out his hand and gripped the back of the car.  Then his knee touched something—­a chain.  He caught it with his other hand.  He lay there, crouching, gripping wherever he could, his fingernails breaking, an intolerable pain in his knee, death spinning on either side of him....

* * * * *

Back behind the tower, Red Gallagher and his mate bent with horrified faces over the body of the signalman.

“What the hell did you want to plug him for?” the latter muttered.  “He ain’t in the show at all.  You’ve done us, Red!  He’s cooked!”

Red Gallagher staggered to his feet.  Already the horror of the murderer was in his eyes as he glanced furtively around.

[Illustration:  Quest jumps from the signal tower on to the fast moving train.]

[Illustration:  A pair of mysterious hands place the black box on Quest’s table.]

“I never meant to drop him,” he muttered.  “I got mad at seeing Quest get off.  That man’s a devil.”

“What are we going to do?” the other demanded hoarsely.  “It’s a quiet spot this, but there’ll be some one round before long.  There goes the damned signals already!” he exclaimed, as the gong sounded in the tower.

“There’s the auto,” Gallagher shouted.  “Come on.  Come on, man!  I can fix the tire.  If we’ve got to swing for this job, we’ll have something of our own back first.”

They crawled to the side of the road.  Gallagher’s rough, hairy fingers were still trembling, but they knew their job.  In a few minutes the tire was fixed.  Clumsily but successfully, the great Irishman turned the car round away from the city.