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, and become a resident of 'Planet Normal' like everybody else. 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, Fiona is selected to infiltrate the fraudsters' operation. Posing as a meek former payroll clerk now forced to work as a cleaner, Fiona Griffiths becomes Fiona Grey, hoping the criminals will try and recruit her - knowing that if they discover her real identity, she's dead meat. But as Fiona penetrates deeper into their operation, coming closer to identifying the mastermind behind it, she faces another, even more frightening danger - that her always fragile grip on her sense of self has now been lost and she may never find her way back.