The Neptune File tells the story of the gifted mathematician John Couch Adams and the discovery of the planet Neptune in 1846. Combining scientific triumph with international controversy, this is an intriguing tale of the search for an unseen planet, and the uproar it caused. More than just an intriguing historical yarn, Adam's work signified the beginning of a new era of planet hunting by providing astronomers with a powerful tool with which to search for new worlds. It marked the genesis of the idea that astronomers could find new planets by looking for their telltale gravitational influence on other bodies, rather than observing them directly with telescopes. In recent years this approach has led to an extraordinary series of discoveries - today's planet detectives are relying on a technique whose theoretical foundations were laid by their 19th-century predecessors.