Radioastronomer John Martels falls 25,000 years futurewards, where, camped in the brains of a haughty, bodiless oracle, a jungle tribesman, and a powerful computer, he helps humanity battle the evolved, malevolent Birds. Highly literate, esoteric, and (after a dull start) vivid: theories of telepathy and maps of Mind to delight metaphysicists, while all will enjoy a delightfully sensuous jungle and a Poe-spooky Fortress of the Birds.