The shadow grew until it became a wall of purple-blue from earth to sky. The first plane was quite close to it, diving down into the vapor. Suddenly the ship rocked violently and swung earthward as if out of control. Then it straightened and turned back. Garin could hear Farson demanding to know what was the matter. But from the first plane there was no reply. As Farson's plane kept going Garin throttled down. The actions of the first ship indicated trouble. What if that haze were a toxic gas? "Close up, Featherstone!" barked Farson suddenly. He obediently drew ahead until they flew wing to wing. The haze was just before them and now Garin could see movement in it, oily, impenetrable billows. The motors bit into it. There was clammy, foggy moisture on the windows. Abruptly Garin sensed that he was no longer alone. Somewhere in the empty cabin behind him was another intelligence, a measuring power. He fought furiously against it--against the very idea of it. But, after a long, terrifying moment while it seemed to study him, it took control. His hands and feet still manipulated the ship, but _it_ flew! On the ship hurtled through the thickening mist. He lost sight of Farson's plane. And, though he was still fighting against the will which over-rode his, his struggles grew weaker. Then came the order to dive into the dark heart of the purple mists. * * * * * Down they whirled. Once, as the haze opened, Garin caught a glimpse of tortured gray rock seamed with yellow. Farson had been right: here the ice crust was broken. Down and down. If his instruments were correct the plane was below sea level now. The haze thinned and was gone. Below spread a plain cloaked in vivid green. Here and there reared clumps of what might be trees. He saw, too, the waters of a yellow stream. But there was something terrifyingly alien about that landscape. Even as he circled above it, Garin wrested to break the grip of the will that had brought him there. There came a crackle of sound in his earphones and at that moment the Presence withdrew. The nose of the plane went up in obedience to his own desire. Frantically he climbed away from the green land. Again the haze absorbed him. He watched the moisture bead on the windows. Another hundred feet or so and he would be free of it--and that unbelievable world beneath. Then, with an ominous sputter, the port engine conked out. The plane lurched and slipped into a dive. Down it whirled again into the steady light of the green land. Trees came out of the ground, huge fern-like plants with crimson scaled trunks. Toward a clump of these the plane swooped.