NASA is building a probe to be splashed down in the Kraken Mare, the largest sea on Saturn's great moon, Titan. It is one of the most promising habitats for extraterrestrial life in the solar system, but the surface is unstable and dangerous, requiring the probe to be outfitted with AI software. Melissa Shepherd, a brilliant programmer, has developed 'Dorothy', a powerful, self-modifying AI whose potential is both revolutionary and terrifying. When miscalculations lead to a catastrophe during testing, Dorothy flees into the internet. Former CIA agent Wyman Ford is tapped to help track her down but as he and Shepherd search for the AI, they realise that her horrific experiences in the wasteland of the internet have changed her in ways they can barely imagine, leaving Ford to wonder whether rescuing her is really the right thing.