Russ stoked and lit his pipe, snapped off his machine and swung around in the operator's chair. "Somebody's playing hell with us out around Jupiter," he stated calmly. "I've been expecting something like this," said Greg. "I have been afraid of this ever since Craven blanketed us out of the Interplanetary building." * * * * * "He really must have something this time," Russ agreed. "He's blanketing out the entire Jovian system. There's a space field of low intensity surrounding all of Jupiter, enclosing all the moons. He keeps shifting the intensity so that, even though we can force our way through his field, the irregular variations make it impossible to line up anything. It works, in principle, just as effectively as if we couldn't get through at all." Greg whistled soundlessly through suddenly bared teeth. "That takes power," he said, "and I'm afraid Craven has it. Power to burn." "The collector field?" asked Russ. Greg nodded. "A field that sucks in radiant energy. Free energy that he just reaches out and grabs. And it doesn't depend on the Sun alone. It probably makes use of every type of radiation in all of space." Russ slumped in his chair, smoking, his forehead wrinkled in thought. "If that's what he's got," he finally declared, "he's going to be hard to crack. He can suck in any radiant vibration form, any space vibration. He can shift them around, break them down and build them up. He can discharge them, direct them. He's got a vibration plant that's the handiest little war machine that ever existed." Greg suddenly wheeled and walked to a wall cabinet. From it he took a box and, opening it, lifted out a tiny mechanism. He chuckled deep in his throat. "The mechanical shadow. The little machine that always tells us where Craven is--as long as he's wearing his glasses." "He always wears them," said Russ crisply. "He's blind as a bat without them." Greg set the machine down on the table. "When we find Craven, we'll find the contraption that's blanketing Jupiter and its moons." Dials spun and needles quivered. Rapidly Russ jotted down the readings on a sheet of paper. At the calculator, he tapped keys, depressed the activator. The machine hummed and snarled and chuckled. Russ glanced at the result imprinted on the paper roll. "Craven is out near Jupiter," he announced. "About 75,000 miles distant from its surface, in a plane normal to the Sun's rays." "A spaceship," suggested Greg. Russ nodded. "That's the only answer." The two men looked at one another. "That's something we can get hold of," said Greg. He walked to the ship controls and lowered himself into the pilot's chair. A hand came out and hauled back a lever. The _Invincible_ moved. From the engine rooms came the whine of the gigantic power plant as it built up and maintained the gravity concentration center suddenly created in front of the ship.