Kyreol's small world begins at the Face, a high rock cliff, and ends at Fourteen Falls, a series of rapids. Each year, her people celebrate Moon-Flash-a spark of light that seems to come from and go into the moon, a symbol of life and joy. When a mysterious stranger arrives, Kyreol wants to know more about him, as well as the Moon-Flash, and soon she and her childhood friend Terje leave their home to look for answers. Those answers will pluck Kyreol from Riverworld and transform her life forever-by fast-forwarding her into a future she can barely comprehend.

Kyreol's mission to another planet and Terje's trip to observe their old river home both meet with unexpected dangers and an eventual melding of very different cultures.