Catherine Fisher, the author of the “Oracle-Archon-Scarab” trilogy, which has become a bestseller in many countries around the world, returns to the reader with a new exciting novel in the fantasy genre. Robert, the main character of “Secrets of the Underground Kingdom”, thanks to a meeting with a mysterious druid, ends up to the land of our fantasies, where, between sleep and reality, his younger sister is already located. Overcoming a huge number of obstacles, traps and dangers, Robert tries to find the key to saving the girl.