 What is the flaw in the cousins' plan?
No one, least of all Martin, could dispute that a man's life should be guarded by his kin—but by those who hadn't been born yet? Nobody in the neighborhood was surprised when Martin's mother disappeared and Ninian came to take care of him. He'd been a war baby, born of one of the tides of soldiers—enemies and allies, both—that had engulfed the country in successive waves and bought or taken the women. Besides, if she really was his great-great-grand-daughter, as she said, why would she tell him to call her " Aunt Ninian "? "He's dissatisfied with the current social order and killing you is part of an elaborate plan he's formulated to change it. From time to time, there were other visitors—Uncles Ives and Bartholomew and Olaf, Aunts Ottillie and Grania and Lalage, and many more—all cousins to one another, he was told, all descendants of his. There was no devastation, no war, no unhappiness, none of the concomitants of normal living. It was then that Martin began to realize that either the whole lot of them were insane, or what Ninian had told him at first was the truth. When Martin was sixteen, Raymond took him aside for the talk Ninian had promised five years before. We're virtually the same people ... although it is amazing what a difference two hundred odd years of progress and polish can make in a species, isn't it?" And, on those worlds, it's far cheaper to use native labor than to ship out all that expensive machinery. But he wasn't, for by now he had little respect left for any of his descendants. "Unfortunately, Professor Farkas has just perfected the time transmitter. Conrad's idea had been to go back in time and "eliminate!" In that way, there would be no space-drive, and, hence, the Terrestrials would never get to the other planets and oppress the local aborigines. "It's the adolescent way," he said, "to do away with it, rather than find a solution. "I wormed the whole thing out of him and all of us—the other cousins and me—held a council of war, as it were, and we decided it was our moral duty to go back in time ourselves and protect you." Induced , Martin knew, could have meant anything from blackmail to the use of the iron maiden. "Then we were all ready to forestall Conrad.
 They have kept Martin isolated for almost his entire life, he has no son. Therefore, they will cease to exist.
 Conrad could target their great-great-grandmother and achieve the same result.  Conrad could target their great-grandmother and achieve the same result.  They have kept Martin isolated for almost his entire life, he has no son. Therefore, they will cease to exist.  All Conrad needs to do to find Martin, is to follow the cousins back in time.