A vivid flame spurted from the opposite side of the cutting, followed practically simultaneously by a sharp report that outvoiced the roar of the train. The sentry, without waiting to challenge, had "let rip."
Bringing his rifle to the ready, Terence waited. He had not long to wait. Silhouetted against the gloomy rain-laden sky—for by this time Terence's eyes were used to the darkness—appeared the head, arms and shoulders of a man. In his right hand he held an automatic pistol, and was now blazing away indiscriminately, judging by the splash of flame that stabbed the night in varying directions. He seemed to be leaning over a rock in the side of the cutting with the intention, now that he had been fired upon, to get at close quarters with the sentry.
Bringing his rifle to his shoulder Terence aimed low and pressed the trigger. The fellow gave no convulsive spring; he merely toppled over and fell on the permanent way just as the train emerged, with a rush and a roar and a dense cloud of steam, from the tunnel.
Jerking the lever of his breech-block, the lieutenant inserted a fresh cartridge. He still kept close to the buttress, even after the train had passed. Experience had taught him the necessity for caution in dealing with a wily foe. Not that he feared anything from the man who had been shot. His headlong tumble down the almost precipitous side of the cutting was too realistic for a person shamming death.
The soldier, emerging from his shelter, began to cross the line. Before he was half-way across, another shot rang out from the top of the cutting. The Tommy collapsed in a heap.
Terence let him lie. His whole attention was centred upon the spot from whence the last bullet had sped. With his rifle ready to be lifted to his shoulder, Aubyn waited like a hunter stalking his prey.
He knew that he would not have to wait long. A desperate attempt was being made to destroy the tunnel—an attempt in which the lives of two or more men mattered but little provided success attended the miscreants' efforts. The firer of the last shot, he reasoned, imagined that with the murder of the first sentry, he had only one man to deal with, and now he was lying motionless on the ballast. Thinking that "the coast was clear" the desperado would presently show himself.
A hunched-up shape appeared at the top of the embankment. Some one was descending with his face towards the rock. He was progressing slowly and cautiously, making certain that he had obtained a firm foothold before he groped for a lower one. Every now and then he would turn his head and look towards the doubled-up body of the sentry, till, satisfied that there was no danger in that direction, he gave his whole attention to his descent.
Levelling his rifle, Terence took deliberate aim. He had no qualms in so doing. The fellow was a murderer and train-wrecker, and undoubtedly an agent of the German Government. The lieutenant was alone and unsupported. If he should be "done in" there would be no further obstacle between the miscreant and the success of his diabolical scheme. Besides, there might be more than two men engaged in the enterprise, which, if it matured, might mean the death of perhaps hundreds of human beings.
Terence aimed fairly in the centre of the climber's back. It afforded the best target in the darkness.