The sound grew sweeter as it strengthened, with a queer, inexplicable sweetness unlike any music he had ever heard before, rounder and fuller and more complete than any melody made up of separate notes. Stronger and stronger he felt the certainty that it was the song of some mighty power, humming and throbbing and deepening through the twilight until the whole dim land was one trembling reservoir of sound that filled his entire consciousness with its throbbing, driving out all other thoughts and realizations, until he was no more than a shell that vibrated in answer to the calling. For it was a calling. No one could listen to that intolerable sweetness without knowing the necessity to seek its source. Remotely in the back of his mind Smith remembered the tree-folk's warning, "When Thag calls, you must answer." Not consciously did he recall it, for all his consciousness was answering the siren humming in the air, and, scarcely realizing that he moved, he had turned toward the source of that calling, stumbling blindly over the flowery sward with no thought in his music-brimmed mind but the need to answer that lovely, power-vibrant summoning. Past him as he went on moved other shapes, little and dark-skinned and ecstatic, gripped like himself in the hypnotic melody. The tree-folk had forgotten even their inbred fear at Thag's calling, and walked boldly through the open twilight, lost in the wonder of the song. Smith went on with the rest, deaf and blind to the land around him, alive to one thing only, that summons from the siren tune. Unrealizingly, he retraced the course of his frenzied flight, past the trees and bushes he had blundered through, down the slope that led to the Tree's hollow, through the thinning of the underbrush to the very edge of the last line of foliage which marked the valley's rim. * * * * * By now the calling was so unbearably intense, so intolerably sweet that somehow in its very strength it set free a part of his dazed mind as it passed the limits of audible things and soared into ecstasies which no senses bound. And though it gripped him ever closer in its magic, a sane part of his brain was waking into realization. For the first time alarm came back into his mind, and by slow degrees the world returned about him. He stared stupidly at the grass moving by under his pacing feet. He lifted a dragging head and saw that the trees no longer rose about him, that a twilit clearing stretched away on all sides toward the forest rim which circled it, that the music was singing from some source so near that--that----