And it was pure, lucky chance. Tom showed them the section of the Map he had examined, with the pinpoint of light representing Roger Hunter's asteroid claim. Then the Map Control officer ... much more alert when he saw Major Briarton ... brought an armload of films up and loaded them into the projector. They stared at the screen, and saw the two pinpoints of light where one was now. "What was the date of this?" the Major asked sharply. "Two days before Dad died," Tom said. "There's quite a distance between them there ... but watch. One frame for every hour. Watch what happens." He began running the film, the record taken from the Map itself, accurate as clockwork. The white dot was moving in toward the red dot at a forty-degree angle. For an instant it looked as though the two were colliding ... and then the distance between them began to widen again. Slowly, hour by hour, the white dot was moving away, off the screen altogether.... The Major looked up at Tom and slammed his fist on the chair-arm. "By the ten moons of Saturn...." he exploded, and then he was on his feet, shouting at the startled Map Control officer. "Get me Martinson down here, and fast. Call the port on a scrambled line and tell them to stand by with a ship on emergency call, with a crack interceptor pilot ready to go. Then get me the plotted orbits of every eccentric asteroid that's crossed Mars' orbit in the last two months. And double-A security on everything ... we don't want to let Tawney get wind of this...." Later, while they waited, they went over it to make sure that nothing was missing. "No wonder we couldn't spot it," the Major said. "We were looking for an asteroid in a standard orbit in the Belt." "But there wasn't any," Tom said. "Dad's rock was isolated, nowhere near any others. And we were so busy thinking of the thousands of rocks in normal orbits between Mars and Jupiter that we forgot that there are a few eccentric ones that just don't travel that way." "Like this one." The Major stared at the screen. "A long, intersecting orbit. It must swing out almost to Jupiter's orbit at one end, and come clear in to intersect Earth's orbit at the other end...." "Which means that it cuts right through the Asteroid Belt and on out again." Tom grinned. "Dad must have seen it coming ... must have thought it was on collision course for a while. But he also must have realized that if he could hide something on its surface as it came near, it would be carried clear out of the Belt altogether in a few days' time." "And if we can follow it up and intercept it...." The Major was on his feet, talking rapidly into the telephone. Sleep was forgotten now, nothing mattered but pinpointing a tiny bit of rock speeding through space. Within an hour the asteroid had been identified, its eccentric orbit plotted. The coordinates were taped into the computers of the waiting Patrol ship, as the preparations for launching were made.