"This way!" Tal hurried to a small building, blasted the lock with his electro. Inside were a score of the three-wheeled, atom powered cars. Minutes later they were speeding away from the city, heading for the outer air-lock of Phobos. They reached the place, and Tal worked over the mechanism until huge metal doors rolled away. They saw the ship that had brought them here, the Unit Twenty-Six of the Martian _Valiant_. But they had no eyes for it now. Several of Gorak's own spacers were there, those with the new-type rocket-tubes which Tal had mentioned. "Tal!" An idea was building up in Ric's mind. "Remember what Kueelo said about their power plant, anchored in the center of Phobos? He said it was reverse gravity, expanding _outward_! What would happen if we drove a spaceship straight into it?" For a moment they looked at each other in delighted silence. "About three hundred miles," Tal said, looking at the gray-blue distances of the hollow world. "And Unit Twenty-Six, here, has a supply of atomo-bombs! We'll have to ride it out there, and then get back before the explosion ... it will take perfect timing ... but it can be done!" * * * * * Feverishly they went to work. First they maneuvered one of Gorak's smaller but speedier ships alongside the Mars spacer, anchored it there with magnetic plates which could be thrown on or off in a split second. But it pointed in a reverse direction, with its prow toward the larger ship's stern. Tal Horan looked to the fuel tanks, gave all the rockets experimental blasts to be sure the feed lines were working. At last all was in readiness. Tal Horan faced Praana. "Wait here in one of the other ships. Don't be nervous. Watch for the explosion. You'll be able to see it. The moment you do, get these rockets warmed up and ready!" She nodded, but her face had gone pale. Suddenly she choked up. "Tal, is--is it necessary?" "It has to be done. This is the quickest and surest way! Don't worry," he took her hands in his. "We'll get back, I promise you!" Quickly he turned away and entered the larger ship where Ric was waiting. "You're a spaceman, Ric; I'm not. You take the controls." Ric nodded grimly. Slowly he threw over the rocket-feed control. Yes, he was a spaceman. He'd handled all types of ships under all conditions, but he knew he'd have to call on every bit of his training now! The rockets throbbed to life. Gradually the ship dragged out of the lock, across the vast ledge toward the inner space. Ric increased the power ... then they were free of the planet's shell and heading toward the center of Phobos! The mass of the smaller ship anchored to them made the controls unwieldy, but Ric was ready for that. What bothered him was that they were fighting gravity all the way--a gravity that _spread outward_ toward them! The result was the same as a blast-off from a gravity equal to that of Mars! But there were other conditions that were not the same.