 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 "? It was safer with Ninian, though, because when he pushed her too far, she would cry instead of mopping up the floor with him. "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. The adults obviously figured that if a one-car family hired private tutors for their kid, there must be something pretty wrong with him. The non-glass part of the house was of neat, natural-toned wood, with a neat green lawn in front and a neat parti-colored garden in back. Though they were in the house with him, in their minds and in their talk they were living in another world—a world of warmth and peace and plenty where nobody worked, except in the government service or the essential professions. 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.
 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.