At the height of a Galactic Empire, a mathematician predicts not only its fall but a galaxy-wide dark age of 30,000 years. His plan, set into motion with butterfly wings, is not to prevent the empire’s fall but to trigger a new, more just, civilization to rise in just 1000 years. Azimov’s epic is amazing if you love high concept sci-fi (less so perhaps if you’re after deep characters or indeed the existence of women).