When DC Fiona Griffiths says 'yes' to her policeman boyfriend, it's an affirmation that she wants finally to put her psychological breakdown behind her. But she still can't resist the challenge of an undercover policing course, and finding it remarkably easy to assume a new identity, she comes top of the class. So when an ingenious payroll fraud starts to look like the tip of a huge criminal iceberg, she is selected to infiltrate the fraudsters' operation. Posing as a meek former payroll clerk now forced to work as a cleaner, she becomes Fiona Grey, hoping the criminals will try and recruit her - knowing that if they discover her real identity, she's dead meat.