[1][2][3] The Eye in the Door is set in London, beginning in mid-April 1918, and continues the interwoven stories of Dr William Rivers, Billy Prior, and Siegfried Sassoon begun in Regeneration.

Whereas Regeneration is an anomalous, but not unique, mixture of fact and fiction, The Eye in the Door acknowledges real events, including the campaign against homosexuals being waged that year by right-wing MP Noel Pemberton Billing, and the conviction of activist Alice Wheeldon for attempted assassination of Prime Minister David Lloyd George, here subsumed with the character named Beatrice Roper, but the whole remains consistently within the realm of fiction.

This grants Barker more freedom to explore her characters and their actions, the descriptions of which might be considered libellous if attributed to real people.

A major theme of the book, Prior's intense and indiscriminate bisexuality, is effectively contrasted with Rivers's tepid asexuality and Sassoon's pure homosexuality.

Greater fictional scope also permits a deeper treatment of the psychological, political and professional life of the central character, Billy Prior.