* * * * * Fortunately we encountered no one. At his telescope in the peak of the bow, the forward lookout turned and gazed at us curiously. The dim control turret was empty, eerie with the spots of fluorescent light from its banks of instruments. The controls were locked for the vessel's present course. The door oval to the adjacent chart room was open. Mackensie was alone in there, plotting the _X-87's_ future course on a chart. He stared blankly as the grim young Wilson shoved me in upon him. "Caught this damned fellow in the magnet-room, Captain. He's killed Bentley. By God--something queer's in the air this voyage. Bentley murdered--" Mackensie's first stare of startled amusement as I was shoved captive before him, faded into horror. His heavy, square jaw dropped. "Bentley murdered? Good Lord--why--what ..." "Somebody was tampering with the ship's gravity," I murmured swiftly. "I felt it go off in a section of the main corridor--went down to the magnet-room. Bentley's there dead--drilled through the chest--" "Bentley killed? Murder, here on my ship! Why, by the Gods of the starways--" Big Mackensie was momentarily stupified, his eyes widened, his heavy face mottled an apoplectic red with his rush of anger. "I caught this fellow Penelle--" young Wilson began. "Don't be an ass," Mackensie roared. "He's a Government crime-tracker--stationed here on board this voyage--" My gesture tried to stop him. "Easy Captain. Listeners might be on us--" The chart room door, here beside us, which opened onto the superstructure roof, was closed. But the small oval window beside it, also facing sternward, was open. I dashed to it. The dim roof deck seemed empty. I noticed a light in Len Smith's helio cubby. I drew down the metal shade of our window. Whirled back. The astonished young Wilson stared at me in numbed amazement. "They're coming into the open," I murmured. "Look here, Captain, we've got to plan--" "Why--why, good Lord--I thought we were guarding against a plot on the Moon--" "Well, we're not. It's here--now--" I told him what Nina had said; five of the crew. The new men, placed here on board. And how many of the officers might be in it-- "Why--why good Lord--" Mackensie was completely stricken. For an instant that floored me. I saw him now as a Captain of the old school--bluff, roaring; the sort of fellow who on a surface vessel would deal grimly and ruthlessly with mutineers. But he was frightened now; frightened and confused. "Why--why Penelle--you mean to think that here on my ship--" "Ready to strike--now," I murmured. I told him about the burned place on the helio room door. He could only stare, numbed. And now the murder of Bentley--the first tangible attack our adversaries had made. Who were they? Five of the crew--that would include the hunchback Durk ... Mokk, the Martian? Ollog Torio, the pallid Venus man? Some of the other passengers maybe? And of the ship's officers, whom could we trust?