From the beginning they left their great ship open and unguarded while they commuted back and forth from the airport to the campus. And naturally the government quickly rectified the second error and took instant advantage of the first. A guard was posted around the ship to keep it clear of the unofficially curious, while the officially curious combed the vessel's interior with a fine tooth comb. Teams of scientists and technicians under Matson's direction swarmed through the ship, searching with the most advanced methods of human science for the secrets of the aliens. They quickly discovered that while the star travellers might be trusting, they were not exactly fools. There was nothing about the impenetrably shielded mechanisms that gave the slightest clue as to their purpose or to the principles upon which they operated--nor were there any visible controls. The ship was as blankly uncommunicative as a brick wall. Matson was annoyed. He had expected more than this, and his frustration drove him to watch the aliens closely. He followed them, sat in on their sessions with the scholars at the University, watched them at their frequent public appearances, and came to know them well enough to recognize the microscopic differences that made them individuals. To the casual eye they were as alike as peas in a pod, but Matson could separate Farn from Quicha, and Laz from Acana--and Ixtl--well he would have stood out from the others in any circumstances. But Matson never intruded. He was content to sit in the background and observe. And what he saw bothered him. They gave him no reason for their appearance on Earth, and whenever the question came up Ixtl parried it adroitly. They were obviously not explorers for they displayed a startling familiarity with Earth's geography and ecology. They were possibly ambassadors, although they behaved like no ambassadors he had ever seen. They might be traders, although what they would trade only God and the aliens knew--and neither party was in a talking mood. Mysteries bothered Matson. He didn't like them. But they could keep their mystery if he could only have the technical knowledge that was concealed beneath their beautifully shaped skulls.