They said she wasn't human. They were wrong. A seemingly endless war against the insurgent Crowhoppers keeps the people of Moontown fighting when they'd rather be mining valuable Helium-3. Crater Trueblood's valiant efforts against the genetically-manipulated beings weighs heavily on his mind. What is he really fighting for? In the midst of a deadly battle, Crater captures an enemy Crowhopper. But this one he refuses to kill. "It" is genetically more human than not and its gender seems to be female. She calls herself Crescent. Crater takes her to Moontown as a prisoner of war, but treats her kindly. However, at the hands of Moontown residents Crescent experiences prejudice and even cruelty. Soon Crescent is imprisoned for a murder she didn't commit. Crater comes to her aid, and the two become fugitives, escaping into the vast expanse of hostile terrain called "the big suck." For Crater, it turns out the cause most worth fighting for may be right by his side.