A philosophical allegory that follows a boy who, raised alone on a deserted island, learns by observation and introspection to master the natural world and, step by step, arrives at metaphysical truths — including the unity and providence of the Divine — through pure reason and mystical insight; later encounters with an ascetic mentor and mainland society highlight tensions and harmonies between natural religion, revealed faith, and social conventions, probing how human reason, experience, and tradition contribute to spiritual and intellectual perfection.