The captain of the _Siegfried_ squinted at the tables the navigator had handed him, mentally translating their figures into acceleration units. The ship was only an hour from the assigned point in space, and it was necessary to make a final, ultimately correct alignment, in which seconds of arc meant miles of displacement in the dispersion of the dust on Earth's surface. The captain's concentration was disturbed by the nagging conviction that something was amiss--or had been amiss a minute or so earlier--about his familiar control room. For a moment he had fancied that the door to the sternward-descending stairshaft was standing open; but it was obviously closed.... He put the doubts angrily out of his mind, frowned at the papers, and ordered the expectant pilot: "_Funf Minuten sechsunddreissig Sekunden dritter Geschwindigkeit dem Backbordgetriebe!_" They were not very inspired last words, but he had no chance to make additions, for in the next instant Kane's sharp knife sank between his ribs. The captain gurgled in an oddly muffled fashion and would have fallen, save that invisible hands caught and lowered him. The navigator, looking straight at him, finally realized something had happened. He opened his mouth to cry out, but his throat was cut from ear to ear and no sound emerged. The pilot, about to press the buttons that would wake the portside rocket bank, was stupefied to see that his hand hung over the controls and refused to move as if paralyzed. Enveloped in the mind-numbing field of an invisibility unit at full power, he did not feel the grip that held him or the knife-thrust that killed him. The four Americans switched off their units and indulged in the luxury of removing the metal-stiffened hoods. They had no more to fear aboard the _Siegfried_; two other members of the crew had already been disposed of in the cabins below, and now even if all Germany had known of their presence aboard the dust ship--no method had ever been devised for attacking a ship in space. But they did not exchange many words. There was work that desperately had to be done as the _Siegfried_ drove toward its rendezvous. Kane flung himself into the navigator's seat, and glancing ever and anon at the figures for the original course, began to punch keys on the calculator. Manning hunched over the controls, continuing an intensive study that had begun over the German pilot's shoulder. And Vzryvov stationed himself before a black box fixed to the wall beneath a large clock and conspicuously sealed with a _Hakenkreuz_. Dugan was left without a job; but he was content to slump into an unused seat and think queasily of Earth thousands of miles below. He was out of his element here--but so were the others. None of them had ever been into space before; only Kane had a theoretical acquaintance with rocket navigation.