They stood on the roof of the largest and central building, a low metal structure with four wings, crossing at right angles to make the figure of a great plus mark. The hub was probably Dr. Ku's chief laboratory, Carse conjectured. On each side stood other buildings, low, long, like barracks, with figures of coolies moving in and out. Workshops, living quarters, power-rooms, he supposed: power-rooms certainly, for a soft hum filled the air. There were two great port-locks at ground level in the dome, one on each side, each sizable enough to admit the largest space-ship and each flanked by a smaller, man-sized lock. To reach them.... "And over there," Dr. Ku's voice broke in, "you see your borrowed ship, the _Scorpion_. But please don't let it tempt you to cut short your visit with me, my friend. It would avail you nothing even if you reached her, for it requires a secret combination to open the port-locks, and my servants' brains have been so altered that they are physically incapable of divulging it to you. And of course I have offensive rays and other devices hidden about--just in case. All rather hopeless, isn't it? But surely interesting. "Let us go: I have more. Below, in my main laboratory in the center of this building, there's something far more interesting, and it concerns you, Carse, and me, and also Master Scientist Eliot Leithgow." He let the words sink in. "Will you follow me?" And so they went below again, down the spider ladder into the corridor. There was nothing else to do: the guards, ever watchful, pressed close behind. But a tattoo of alarm was beating in Hawk Carse's brain. Eliot Leithgow again--the hint of something ominous to be aimed at him, Carse, for the extraction of information he alone possessed: the whereabouts of his elderly friend the Master Scientist. CHAPTER V _The Color-Storm_ The corridor was stopped by a heavy metal door. As the small party approached, it swung inward in two halves, and a figure clad in a white surgeon's smock emerged. He was a white man, tall, with highly intelligent face but eyes strangely dull and lifeless, like those of the coolie-guards. His gaze rested on Ku Sui, and the Eurasian asked him: "Is it ready?" "Yes, lord,"--tonelessly. "Through here, then, my friends." The door opened and closed behind them as they stepped inside. "This is my main laboratory. And there, friend Carse, is the object which is to concern us."