Away they ran lightly, out into the sunshine, happy to be in the warm, scented air, through the garden, off to the dear old rocks which were already drying nicely, and at once a fine game of hide-and-seek was in full swing.
Dulcie had gone again to hide, and Cyril had his face buried in his hands, waiting for the familiar "Cuckoo!" when he was startled instead by a faint cry of surprise, followed by "Cyril, come quick! Quick!"
"It must be a beetle or a toad, or something," he said to himself as he hurried to the spot from which her voice seemed to come; but it was only after she had repeated her excited cries that he found her at last.
She had found a passage through the rocks which they had never noticed before!
"Come along!" cried Cyril joyously at the sight of it. "Come along! we'll go on a voyage of discovery!"
Down the passage they went, far and carefully, for there was only a glimmer of light in a thin streak peeping through, because the rocks all but joined at the top, and the ground was uneven and slippery. But in spite of their caution they got a sudden start, for they became aware of a silent brook flowing deep and swiftly by, at their feet: another step and they would have been in it. The Twins, rather startled, looked at one another, and then without further thought they just jumped across. Jumped into an open space—into Moonlight. There was actually a full moon overhead, but with such seams and lines about it that it bore the appearance of being pieced together like a geographical puzzle.
"Cyril, look there!" whispered Dulcie, pressing close up to him, as soon as she found words.
In the white light there stood an immense rock. In it there was a wooden door with hewn-out steps leading up to it. A nice red door it was, with a green knocker upon it in the shape of a mouth smiling a welcome. Of course they went up to it, climbed the steps, which were high and difficult, and stared at the neatly engraved brass plate below it, which bore the words:
Knock if an answer is required.
If not, why?