She neutralized her controls as she felt the mighty beams of the landing engine take hold of her little ship. Upon previous visits she had questioned nothing--this time she was questioning _everything_. Was she landing, or not? Directing her every force inwardly, she probed her own mind to its profoundest depths. Definitely, she was her own mistress throughout--no conceivable mind could take _hers_ over so tracelessly. As definitely, then, she was actually landing. She landed. The ground upon which she stepped was real. So was the automatic flier--neither plane nor helicopter--which whisked her from the spaceport to her familiar destination, an unpretentious residence upon the grounds of an immense hospital. The graveled walk, the flowering shrubs, and the indescribably sweet and pungent perfume were real; as were the tiny pain and the drop of blood which resulted when a needle-sharp thorn pierced her incautious finger. Through automatically opening doors she made her way into the familiar, comfortable, book-lined room which she knew was Mentor's study. And there, at his big desk, unchanged, sat Mentor. A lot like her father, but older--much older. About ninety, she had always thought, even though he didn't look over sixty. This time, however, she drove a probe--and got the shock of her life. Her thought was stopped--cold--not by superior mental force, which she could have taken unmoved, but by a seemingly ordinary thought-screen; and her fast-disintegrating morale began visibly to crack. "Is all this ... are you ... real, or not?" she burst out, finally. "If it isn't, I'll go mad!" "That which you have tested--and I--are real, for the moment and as you understand reality. Your mind in its present state of advancement cannot be deceived concerning such elementary matters." "But it all wasn't, before? Or don't you want to answer that?" "Since the sure knowledge will affect your growth, I will answer. It was not. This is the first time that your speedster has landed physically upon Arisia." The girl shrank, appalled. "You told me to come to you again when I had learned that I did not know everything there was to know," she finally forced herself to say. "I learned that in the tube; but I did not realize until just now that I don't know _anything_. Do you really think, Mentor, that there is any use at all in going on with me?" she concluded, bitterly. "Much," he assured her. "Your development has been eminently satisfactory, and your present mental condition is both necessary and sufficient." "Well, I'll be a spr--" Kathryn bit off the expletive and frowned. "What were you doing to me before, then, when I thought I got everything?" "Power of mind," he informed her. "Sheer power, and penetration, and control. Depth, and speed, and all the other factors with which you are already familiar." "But what is left? I know there is--lots of it--but I can't imagine what."