"By the way, Mike," he said, when they had alighted opposite the hangar, "don't say anything about those lights we saw on the bridge. I'm going to investigate the matter myself."
Mike readily promised, and Lawless was strolling away when a thought suddenly struck him.
"By Jove!" he ejaculated aloud. "I believe I've got it!"
His memory had flashed back to the notice he had read, offering a reward in connection with certain paint marks on the Forth Bridge. No doubt the misguided "person or persons" who had daubed the bridge had used luminous paint. This, of course, would explain the phosphorescent glow which had so puzzled him.
The question now was, had it been done merely as a joke or for some specific object? If for a joke, it was difficult to see where the humour came in; if for an object, it was equally difficult to see what purpose it could serve.
"I'll have a closer look at the bridge when I've rested a bit," he told himself.
That afternoon the Lieutenant took a train to Queensferry. He then set out to walk back over the bridge along the railway track. The paint daubs were clearly visible, though not, of course, phosphorescent in the daylight. It struck him as peculiar that these marks had a definite shape, or rather two definite shapes. One took the form of a St. Andrew's Cross, the other the form of a star—that is, instead of two intersecting lines of the same length, there were four.
But that was not all. A careful examination showed that these stars were placed at the weakest part of the bridge; in other words the parts which would be easiest to destroy by means of dynamite. Finally, the marks could only be seen from above the bridge, not from below it.
Lawless whistled softly when he had made these discoveries.
He returned to the depot, and went at once to his commanding officer and told him of the discoveries he had made. He also explained at some length his own theory concerning them. The commanding officer listened patiently at first because he was a good-natured fellow and liked to see his officers exercise initiative and resource. But his interest in the story soon flagged, and when Lawless began to state his deductions it wilted entirely. An expression of resigned boredom appeared on the officer's face and remained there till the interview came to an end.