In "Crack Down," Val McDermid emphasizes the importance of adaptability for private investigators. She suggests that to succeed in this field, one must be able to blend seamlessly into different environments, much like a chameleon. Investigators who draw attention to themselves may fail to serve their clients effectively.

The message highlights the need for discretion and the ability to navigate various social settings without being conspicuous. It underscores the idea that standing out can be detrimental, as it impairs the investigator's ability to gather information and accomplish tasks without arousing suspicion.