Warning: wikipedia contains spoilers
The plot revolves around an actual incident which occurred in 1917, when the poet, Siegfried Sassoon, who had been decorated for bravery during his service on the Western Front, suddenly decided to protest against the war. As a result, he was sent to Craiglockhart War Hospital near Edinburgh, to be treated for "neurosis" by the pioneering psychoanalyst, W. H. R. Rivers.
Several of the characters in the book are real people, including Rivers and Sassoon, the poets Robert Graves and Wilfred Owen, and doctors who actually worked at Craiglockhart. Other patients are based on Rivers' most well-publicised case histories. However, one of the central characters, the working-class officer Billy Prior, is entirely fictional. Prior arrives at the hospital having lost the power of speech, as a result of a traumatic experience which Rivers gradually uncovers, but is at first hostile and defiant. His relationship with Sarah, a worker in an ammunition factory, is explored, throwing some light on his almost schizophrenic personality.
Barker went on to use Prior as the antagonist of two sequels, The Eye in the Door and The Ghost Road.
A 1997 film was made of the book (entitled Behind the Lines in the USA). It starred Jonathan Pryce as Rivers and Jonny Lee Miller as Prior.
A contemporary depiction of shell shock is Rebecca West's novel The Return of the Soldier (1918), which was filmed in 1982 by Alan Bridges with Alan Bates in the title role.