Johannes Kepler starts out as an astrologer casting horoscopes for a living, and ends up discovering the laws that describe how every planet moves. Carl Sagan narrates Kepler's path from mystical number-mongering, he first tries to fit the planets into nested Platonic solids, to the three laws he eventually derives from Tycho Brahe's decades of naked-eye observations: orbits are ellipses, not circles, and a planet sweeps out equal areas in equal time no matter where it sits in its path. Sagan also stops on the darker turns of Kepler's life, including the witchcraft trial brought against his mother, to show how precarious reason was in his era. The episode traces the shift from a universe explained by divine harmony to one explained by mathematics that actually predicts where a planet will be next Tuesday. Animated star fields, planetary models, and Sagan's own readings of Kepler's writing carry the science, building toward the idea that the same laws governing Mars govern falling apples on Earth.