The Magic Labyrinth (1980) is a science fiction novel by American writer Philip José Farmer, the fourth in the series of Riverworld books. The title is derived from lines in Sir Richard Francis Burton's poem The Kasîdah of Hâjî Abdû El-Yezdî: Originally intended to be the final book in the series, this book continues the chronicles of the adventures of Sir Richard Burton, Cyrano de Bergerac, Alice Liddell, Tom Mix, and Samuel Clemens through a bizarre afterlife in which every human is simultaneously resurrected along a single river valley covering an entire planet. Many questions about the creation and purpose of the Riverworld are answered, but several are left unanswered, prompting Farmer to write a fifth and final novel, Gods of Riverworld, in 1983. Edgar L. Chapman wrote a 1984 biography of Farmer entitled The Magic Labyrinth of Philip José Farmer. Plot The book begins with the Mysterious Stranger, known as X, the renegade Ethical (one of the Riverworld's creators) who posed as the engineer Barry Thorn on the airship Parseval and there murdered Milton Firebrass and several others, all of whom were fellow Ethicals. He is now posing as a Mayan named Ah Qaaq, in the company of the Chinese poet Li Po. Through his internal reverie he reveals that his identity was discovered by Monat Grrautut, the director of the Riverworld project, who recalled 'X' to the Dark Tower to be judged. Against this, 'X' used a remote command to kill all the inhabitants of the tower and stop the resurrections of Riverworld's inhabitants. His reverie when the left bank's 'grailstones' (supplying food and stimulants) fail to operate and are not mended by the Ethicals, who are either dead or confined (like 'X' himself) to the river. After the grailstones fail, the inhabitants of the left bank invade the right for resources, and half of humanity dies in the conflict. Concurrently, protagonist Richard Burton and his friends have joined the crew of King John's ship, the Rex Grandissimus, where Burton, masquerading as a Dark Age British warrior, becomes King John's security chief. One day Tom Mix, Jack London, and Peter Jairus Frigate apply to join the crew; and Burton, recognizing Frigate, attacks him as a spy for the Ethicals. Realizing his mistake, Burton allies himself with Frigate, Mix, and London. Meanwhile, the Ethical Monat Grrautut has boarded Sam Clemens' ship, where he is murdered by the renegade Ethical.