Four hundred years in the future, genetic engineering has created three species of humans. Homo sapiens – the Sapes – are the masters. The Sirians are savage and insular. The Helots are slaves, denied even the right to breed. Now, after generations of abuse and exploitation, the Helots seek to overthrow their masters by attacking Zeus, the supercomputer that oversees the Sapes' society.

For Maddy Hawthorn, a Sape colonist, the peaceful life she had planned at Barnard's Star is torn apart when she becomes involved in the Helot's terrorist plot to destroy the stranglehold of the Elite over the other races. Reluctantly, she joins up with insurgent Helot Igil Hoo and renegade Sirian Dorac Elsilunda. Together, they are forced to work for the revolution.

Soon they are sent on a suicide mission to destroy Zeus. Trying to stop them is Agnes Lawson, a navy commander who finds herself sympathizing more and more with the rebels. On a remote planet called Lizard all four find themselves facing not only formidable military opposition but also fundamental questions about their own motives, as well as the nature of the society which has made them who they are.