"Come on!" exclaimed Ross, breaking into a run.
Concealment was no longer necessary. Should occasion arise, there would be plenty of help forthcoming, for there were several dock policemen and soldiers on duty close at hand.
Von Ruhle had increased his pace into a brisk walk when he heard the noise of his pursuers. Then he, too, began to run.
"Stop him!" shouted Trefusis, calling to a group of uniformed men standing in front of an abattoir.
Turning, the German made towards the quay-side. He was no match in speed for his youthful pursuers; but he gained the water's edge before Ross headed him off.
"Give in, von Ruhle!" he challenged.
The spy recognized the voice of the British lad whom he imagined to be miles away, on board an unterseeboot.
With a quick movement, the spy plucked a leather case from his coat pocket and hurled it over the edge of the quay, then, throwing up his arms, he dropped lifeless upon the rain-sodden ground.
Rapidly a crowd collected. Amongst them was Detective-inspector Ferret, who, having finished his conversation with his luckless confrère, was leaving the post office when he heard the commotion.
"Well, what's all this?" he asked brusquely. He bent over the body of the spy and flashed a pocket-lamp upon his face. "It's our man," he continued, addressing the lads in an undertone. This remark was needless, since they were already certain upon that point. "He's done us out of a job. Heart disease? No fear: it's poison. Don't wait here. Your work in this direction is done. I have still a few unpleasant tasks to perform. Cut off to the hotel and await me there. I may be an hour."