Stan and Estrella, two young people from Earth, journey to the Gateway asteroid looking for adventure, and discover each other during a flight in one of the ships the alien Heechee left behind when they explored our Solar System. Stan and Estrella settle among the Heechee on a planet in the galactic core, never suspecting that the two of them may be the last, best hope to save the humans and Heechee in the core from destruction by a crazed madman. Wan Enrique Santos-Smith, a man full of loathing for the Heechee, will stop at nothing to destroy the Heechee and their human friends. But Stan and Estrella, with the help of a fabulously wealthy philanthropist and the unique machine mind Marc Antony, are determined to thwart Wan's terrible plan. At stake is nothing less than the fate of all life in the galaxy.