The Limbo Line is a 1963 spy thriller novel by the British writer Victor Canning.Burton p.21 A former British secret service agent Richard Manston is called out of retirement to tackle a Soviet spy network kidnapping recent defectors to be taken back to Moscow.
The book acts as a prequel to the four Rex Carver novels in that it introduces the Government agency that Carver is later unwillingly drawn into. Manston also appears as a character in some of the Rex Carver books.Higgins, John. A Rex Carver Companion (2009)
Film adaptation In 1968 the novel was turned into a film of the same title directed by Samuel Gallu and starring Craig Stevens and Kate O'Mara.Goble p.69 The story was reissued by Pan Books as a tie-in with the film release.
References
Bibliography Burton, Alan. Looking-Glass Wars: Spies on British Screens since 1960. Vernon Press, 2018. Goble, Alan. The Complete Index to Literary Sources in Film. Walter de Gruyter, 1999.