Lieutenant MacWhirlie had now almost come to doubt so much of his theory as located the unknown enemy within the picket line. But he was a persistent person, and disliked to give up his theory until he had something better to lay hold of. Moreover, as he still believed the Pixies to be the cause of the late misfortunes, and as he knew they were wont to be quite active about the peep of day, he resolved to bide by his voluntary watch a little longer. He beckoned Sergeant Vigilant to his side and the two sat down to rest among the delicate ferns that covered the ridge. They went over again the events of the night, putting this and that together, in order to frame some intelligent theory for their guidance. MacWhirlie, however, could find nothing to shake his first conclusion.
"The danger must have come upon them unawares," said he; "it was clearly in every case a complete surprise. If an enemy had approached from the front, he would have been spied in time for an alarm. A surprise so thorough could only have come from the direction of our own camp, as that was the only quarter not carefully watched."
The Sergeant's reply was arrested by a curious phenomenon. The ground beneath them seemed to be trembling; it raised slowly, swayed back and forth, and then sank down. The Brownies jumped to their feet and MacWhirlie exclaimed:
"What is that? Did you notice the shaking of the earth? or was it only the grass rocking in the wind?"
"It was—it seemed to be an earthquake," answered Vigilant. "There! I feel the ground again trembling beneath us."
Fig. 117.—A Trap-door Opened.
The earth had, indeed, begun to lift up like a wave; higher and higher it rose, until the officers, finding that they were losing their perpendicular, flung themselves backward, in true Brownie fashion, into a bush on the summit of the ridge.
"See!" cried MacWhirlie, clasping the Sergeant by the arm, "there is the enchantress of your haunted ground!"