Heavily influenced by Doyle’s growing belief in Spiritualism after the death of his son, brother, and two nephews in World War I, the book focuses on Edward Malone’s at first professional, and later personal interest in Spiritualism. This is the third and last novel in the „Professor Challenger” series, and is a marked departure from the previous tales. Professor Challenger and Malone return for the adventure, this time exploring the spiritual world. Malone, along with Challenger’s daughter Enid, starts investigating spiritualist meetings for his newspaper. Initially a skeptic, he soon discovers that the spiritualists are right. But can he convince Professor Challenger of the same thing?