The Door Through Space is a science fiction novel by American writer Marion Zimmer Bradley.

The novel spins around an intelligence agent and a blood feud in the Dry Towns in the north of a world called Wolf.

At one time Race Cargill had been the best Terran Intelligence agent on the complex and mysterious planet of Wolf. He had repeatedly imperiled his life amongst the half-human and non-human creatures of the sullen world. And he had repeatedly accomplished the fantastic missions until his name was emblazoned with glory. 

But that had all seemingly ended. For six long years he'd sat behind a boring desk inside the fenced-in Terran Headquarters, cut off there ever since he and a rival had scarred and ripped each other in blood-feud.

But when THE DOOR THROUGH SPACE swung suddenly open, the feud was on again—and with it a plot designed to check and destroy the Terran Empire. (original book blurb)

Although it is not part of her Darkover book series, Darkover is mentioned (as another planet) in passing in the book; numerous Darkover elements appear in the book, such as a red sun, Dry Towns with chained women, catmen and other nonhumans, Terran Empire trade cities and Ghost Wind.

The novel is an expansion of Bradley's story Bird of Prey (which first appeared in the May, 1957 issue of the magazine Venture), it is her first novel, and was first published in book form in 1961.

Marion Eleanor Zimmer Bradley (1930-1999) was an American author of fantasy novels such as The Mists of Avalon and the Darkover series.