Earth's colonists have divided into the Swimmers, who spend their entire lives in zero-gravity and claim to be the next step in evolution, and the planet-dwelling Walkers. The Swimmers regard those who prefer to live on the surface of a planet as little better than unevolved apes, while the Walkers are not about to say farewell to the planets they grew up on, and think the Swimmers are not advanced at all, but merely deranged. Crowell, born a Swimmer but now a Walker by choice, is caught in the middle as the two sides prepare for war. Then he discovers the true cause of the altercation: a hidden alien race trying to provoke a war of extinction.
James Henry Schmitz (1911–1981) was an American writer born in Hamburg, Germany of American parents.
Schmitz is best known as a writer of so-called "space opera", and for strong female characters (such as Telzey Amberdon and Trigger Argee) that didn't conform to the damsel in distress stereotype typical of science fiction during the time he was writing. His first published story was Greenface, published in August 1943 in Unknown.
Most of his works are part of the "Hub" series, though his best known novel is The Witches of Karres, concerning juvenile "witches" with genuine psi-powers and their escape from slavery. Karres was nominated for a Hugo Award. During recent years, his novels and short stories have been republished by Baen Books, edited and with notes by Eric Flint.
James H. Schmitz. Wikipedia.