The story centres more on his daughter Enid and his old friend Edward Malone. Another friend from the 1912 novel The Lost World, Lord John Roxton, is also involved in the novel's second half. Professor Summerlee, who has died of old age around this time, is referred to by the mediums.
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.