The five stories in In a Glass Darkly reflect a profound and deeply disturbing uncertainty about the nature of humanity and its relationship with spirituality. Originally published separately in magazines, the stories are framed and linked in this collection as cases in the papers of the fictional Dr. Hesselius. Sheridan Le Fanu's approach to the supernatural re-works traditional Irish oral storytelling and combines it with nineteenth-century adaptations of the eighteenth-century Gothic novel.

Appendices include Le Fanu's correspondence about the stories, posthumous assessments of his life and work, and twentieth-century critical commentaries by M.R. James and Elizabeth Bowen. Engravings from the original serial publications of several stories are also included.