A Matter of Time is a novel by Glen Cook, combining elements of science fiction (specifically, time travel), crime fiction and spy thriller. In regard to the last, the novel in particular takes up and expands the theme of American prisoners of war being brainwashed in Communist China and their loyalties reversed – a theme made famous through the novel The Manchurian Candidate and film made on its basis. The book was re-published in 2011, along with other earlier works of Glen Cook.