In The Wilderness

"The Year of the Ransom."

Wanda Tamberly's kidnapper, Castelar, tells Wanda that her Uncle Steve:

"'...is my hostage, left in a wilderness where starvation will soon take him off, unless wild beasts do so first. It is for you to earn his ransom.'" (p. 698)

Castelar, new to time travel, has grasped one of its paradoxes. When the only kind of travel that is involved is through three-dimensional space - whether across the Earth's surface, through the air or between planets - if a captor spends an indefinite period of time away from the wilderness where he has left his hostage, then that hostage can be expected to starve or to be killed by animals. (In fact, Steven Tamberly is resourceful enough to survive but, for the moment, we are reasoning from Castelar's premises.) Since in this case time travel is involved, Castelar can spend any length of time - even years or decades - away from the wilderness and yet can return there soon enough to rescue his hostage. At any time between now and his death, Castelar, provided of course that he retains the timecycle, can decide whether it has been the case that his hostage was left for only a short time in the wilderness or for an uncomfortably long time or was just left there to die. Castelar does not yet know which of these eventualities happened to the hostage but at any time he can decide which - and that is odd.

I used to imagine a time traveller spending a week in the twenty-first century and of his friends in the twentieth century waiting a week for him to return and, of course, they might for some reason decide to do it that way.