 How does Conrad go back in time?
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? 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. "He's dissatisfied with the current social order and killing you is part of an elaborate plan he's formulated to change it. There was no devastation, no war, no unhappiness, none of the concomitants of normal living. "And Conrad really got upset over the way Earth has been exploiting the not so intelligent life-forms on the other planets," Raymond continued. "We just come a couple of centuries or so later, that's all. 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. I don't mean in the now for me, but the now for you," Martin explained laboriously. Unaware of the near-contempt in which his young ancestor held him, Raymond went on blandly: "Anyhow, Conrad took it upon himself to feel particularly guilty, because, he decided, if it hadn't been for the fact that our great-grandfather discovered the super-drive, we might never have reached the stars.
 Conrad built a time transmitter using a copy of Professor Farkas' plans.
 Conrad stole Professor Farkas' time transmitter to send himself back in time.  Professor Farkas sent him back in time with the time transmitter.  Conrad built a time transmitter using a copy of Professor Farkas' plans.  Professor Farkas' assistant sent Conrad back in time using the time transmitter after Conrad gave him a bribe.