But just as he was rising to call her, he noticed something far down the track that caused him to drop back again.
"They're smuggling a machine-gun into position!" he cried.
He had caught a glimpse of the barrel projecting over a ledge of rock. With instant decision he trained his own gun upon it, and before it could open fire, he pumped out a hail of lead that struck it from its position, and the men serving it, in spite of their shield, were killed or disabled either by direct shots, ricochets, or splinters.
"One belt empty!" he said, as he replaced it with a full one. "By George! Now we're in for it!"
He had heard the characteristic scream of a shell. Immediately afterwards there was a terrific explosion, and he saw a tall column of smoke, stones, and dust shoot into the air from the rocks not two hundred yards away. In another half-minute another shell exploded, a little nearer.
"They must be 'phoning the range," he said. "Look here, Enderby, I must get you out of it. I can't leave the machine-gun now, but the Serbs must carry you away. Marco Kralevich!" he shouted.
The old man hurried down.
"They'll have the range in a few minutes," said Burton. "I want you and your friend to carry Captain Enderby out along the track yonder, towards where the prisoners are. Take your daughter, too. When you come back, go down into the cellar and relight the train; it must have gone out. They will smash the tower; the only chance of holding them up is to explode the mine. Make haste, for Heaven's sake!"
Marco summoned Nuta and Milosh from the roof. They lifted Enderby, and were half-way down the stairs with him when the Bulgarian gunners made their first hit. A shell carried away a corner of the parapet. The tower shook under the explosion, and the falling masonry plunged into the enclosure, raising a dense cloud of dust. Burton trembled for the safety of his friends, but his thoughts were taken from them by a renewed movement among the enemy. Immediately after the crash, the men concealed in the bushes sprang out, and dashed forward with a cheer. They would have been wiser to wait. Burton saw them indistinctly through the dust, but he had the range to a yard, and again they melted away under his withering fire.
Shells were now bursting around the tower. There was another crash above; fragments of stone fell into the room, striking Burton in many places. It was a moment of racking anxiety. He dared not leave the gun until the track had been destroyed, yet the tower might crumple down upon him. His ammunition was running short--would Marco get back in time? Even if he relit the train, would the flame reach the explosives? And at that crisis he nerved himself for what must be regarded as a supreme act of self-sacrifice. If all else failed, at the last moment he must go himself into the cellar, and fire into the charge.