This novel is loosely based on two novellas originally published in Analog. Polly is a fighter pilot and she has coped fine with all sorts of enemies. On Cynthia, she finds herself faced with a new enemy. They fly and they are deadly and they are not supposed to be there. Settlement on this planet is crucial. Polly finds herself with a horrid choice: Kill so that generations of human and Cynthian children can survive.
