"But he said Dr. Mansard was his father," protested Trella. "Robots and androids frequently look on their makers as their parents," said Jakdane. "Quest may not even know he's artificial. Do you know how Mansard died?" "The oxygen equipment failed, Quest said." "Yes. Do you know when?" "No. Quest never did tell me, that I remember." "He told me: a year before Quest made his rocket flight to Ganymede! If the oxygen equipment failed, how do you think _Quest_ lived in the poisonous atmosphere of Jupiter, if he's human?" Trella was silent. "For the protection of humans, there are two psychological traits built into every robot and android," said Jakdane gently. "The first is that they can never, under any circumstances, attack a human being, even in self defense. The second is that, while they may understand sexual desire objectively, they can never experience it themselves. "Those characteristics fit your man Quest to a T, Trella. There is no other explanation for him: he must be an android." * * * * * Trella did not want to believe Jakdane was right, but his reasoning was unassailable. Looking upon Quest as an android, many things were explained: his great strength, his short, broad build, his immunity to injury, his refusal to defend himself against a human, his inability to return Trella's love for him. It was not inconceivable that she should have unknowingly fallen in love with an android. Humans could love androids, with real affection, even knowing that they were artificial. There were instances of android nursemaids who were virtually members of the families owning them. She was glad now that she had not told Quest of her mission to Ganymede. He thought he was Dr. Mansard's son, but an android had no legal right of inheritance from his owner. She would leave it to Dom Blessing to decide what to do about Quest. Thus she did not, as she had intended originally, speak to Quest about seeing him again after she had completed her assignment. Even if Jakdane was wrong and Quest was human--as now seemed unlikely--Quest had told her he could not love her. Her best course was to try to forget him. Nor did Quest try to arrange with her for a later meeting. "It has been pleasant knowing you, Trella," he said when they left the G-boat at White Sands. A faraway look came into his blue eyes, and he added: "I'm sorry things couldn't have been different, somehow." "Let's don't be sorry for what we can't help," she said gently, taking his hand in farewell. Trella took a fast plane from White Sands, and twenty-four hours later walked up the front steps of the familiar brownstone house on the outskirts of Washington. Dom Blessing himself met her at the door, a stooped, graying man who peered at her over his spectacles. "You have the papers, eh?" he said, spying the brief case. "Good, good. Come in and we'll see what we have, eh?"