So Jacqueline acquiesced, and watched her brother row away with much trepidation and many muttered prayers for his safety. Darkness soon shut each boat from the sight of the other, but Gysbert paddled on keeping clear of floating debris as best he could, and trying hard to ascertain through the blackness just what was his location. Several times he found himself far out of his course, and thus more than one valuable hour was lost. At length, however, the water became too shallow to continue rowing, and he disembarked, tying the boat to a tree. By several signs he recognized the spot to be near where he had come out of the hidden tunnel, several weeks ago. Of the Spanish army at this spot, there remained but a few stragglers gathering up their possessions.
Gysbert concluded that the safest place for him was the tree to which he had tied his boat, and he was soon among its branches. From here he watched the departure of the last Spaniard, and was just about to descend, when one solitary sneaking shadow attracted his attention. In the blackness of the night he could discover little of its intentions, but as it moved off in the direction of the wall, he decided to get down and follow it. The shadow glided along straight for the wall till it finally disappeared behind the bushes that hid the secret opening. When Gysbert arrived on the spot, there was not even a shadow to be seen. Then a great light dawned on his mind.
"Dirk Willumhoog!" he whispered. "What on earth am I to do now?" For a moment he stood undecided. He dared not venture into the secret passage while his enemy was there. And should Dirk not come back it was still very unsafe, for he might be guarding the other entrance. But the matter was soon to be solved in a way very different from any he could possibly have imagined.
While he stood considering his course, he was startled by a curious rumbling sound that appeared to emanate from the very earth under his feet. Then there were grinding and groaning noises, low and indistinct, but terrifying beyond imagination. Gysbert's hair fairly rose on his head, and something impelled him to beat the hastiest kind of a retreat. Turning on his heel, he ran with all speed to his boat, unmoored it, pushed it off, and rowed far out upon the black water.
Suddenly there was a terrific sound like an explosion, then a crash that shook the earth for miles around, and made Gysbert's little boat rock on the waves till it all but over-turned completely. When the boy recovered himself enough to realize what had happened, it did not take him long to explain the dreadful sounds. Undermined by the stream so long secretly eating at its base, the whole wall of Leyden between the Cow Gate and the Tower of Burgundy had suddenly fallen in utter ruins!