''The Hidden Stream'' by Ronald Knox is a collection of apologetic talks explaining core Catholic doctrines and addressing modern faith challenges, using the metaphor of a secret, nourishing stream flowing beneath Oxford as a symbol for the Church. Knox, a witty convert, covers topics like the nature of religion, miracles, salvation, sacraments, and the resurrection, offering insights for both believers and skeptics with characteristic clarity and humor, making it a guide to Catholic teaching for a new era.