Although this is a Professor Challenger story, it centres more on his daughter Enid and his old friend Edward Malone. Another friend from 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 (much to the anger of Professor Challenger).
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. There is a suggestion in chapter two that the deaths of “ten million young men” in World War I was punishment by the “Central Intelligence” for humanity’s laughing at the alleged evidence for life after death.