Son of the Tree begins with the arrival of Joe Smith on the planet Kyril, so distant that Earth is but a myth. Kyril is dominated by a religious aristocracy called 'Druids', who rule over the five billon commoner 'Laity', and who control worship of the 'Tree of Life' – a huge tree with a trunk five miles in diameter, and height of twelve miles. The Druids are xenophobic, and consider Joe to be a spy. For unknown reasons, he is befriended by Hableyat, a native of the world of Mangtse, self-admitted spy who finds him a job as a chauffer for Druid Princess Elfane.
After witnessing a murder committed by Princess Elfane's lover Manaolo, Joe Smith flees Kyril on the spaceship Belsaurion bound for the world Ballenkarch, his original destination – only to find that his fellow passengers...