In "On the Loose," Christopher Fowler explores the theme of adaptation in one's life. The protagonist's transition into a new phase is less about drastic changes and more about small adjustments to his existing behavior. He possesses a unique skill set that allows him to navigate new situations without drawing attention to himself.

The notion of invisibility is significant in the story, as it reflects the character's ability to blend into his surroundings. This subtlety suggests a mastery of social dynamics, enabling him to maneuver through different environments while maintaining a low profile. Such adaptability is central to his journey and overall character development.