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Eight-year-old Ginny Fitch walks alone on a foggy beach and gradually comes across more and more wreckage that's been washed ashore. It's clear that all the stuff is from a yacht where a children's birthday party had been underway. But quickly it becomes obvious that someone, somewhere, is actually generating Ginny's environment and that there is an insidious goal behind it all.
Two faceless controllers attempt to drive Ginny in a specific direction, but her playful nature makes it harder and harder. As a result, they need to continuously ramp up the danger for her, even to the point of creating a hideous monster to chase her. As Ginny moves through her environment, it constantly changes from beach to dense forest to a futuristic and complex place filled with machinery as the controllers struggle to keep their young charge focused on the goal.
As time seems to be running out, Ginny is finally herded into what appears to be some sort of "sleep chamber" which, although decorated like a little girl's bedroom, is actually the hypersleep cocoon that she will occupy for 1500 centuries.
Revealed at the end is the true nature of Ginny's circumstance. She is the lone human accompanying millions and millions of human embryos that have been sent toward a distant planet, and in 150,000 years when they arrive, she will be responsible for reestablishing the human race.