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. But as she 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.