from the back cover:
As they walk through a park in the distant future, Harl and Ellen talk about their work and their lives. But they will never have a life together because their work as scientists is more important to them than their love. Harl plans to leave Earth, on a long and dangerous journey through space. Ellen plans to stay on Earth, to change the way the human mind works. When Harl returns to Earth, Ellen will be long dead ...and the world will be a very different place.