Detective Sergeant Nancy Devlin is a good cop with a dark secret - a loyalty to haulier and drugs trafficker Frank Le Saux, to whom she has been close since childhood.

Mistrustful of her colleagues, Nancy needs an ally but fears that if she opens up to Hayley it will put them both in danger. Nancy is then unexpectedly forced into the spotlight when the police make a public appeal.

Nancy visits the latest suspect, garage owner and Le Saux associate Duncan Elliot, where she spots Theo Kettler's missing car. A vital piece of evidence is later recovered from the vehicle, giving DCI Newman a breakthrough - but placing Nancy in even greater danger. Meanwhile, tensions surface among the Le Sauxs when Hayley and her brother Tate inherit the haulage yard.

In a reckless bid to accelerate the investigation and turn the tables on the man who may be hunting her, Nancy proposes a risky undercover operation, but soon finds herself caught up in violence she cannot escape.

Nancy finally sees the truth, but struggles to persuade Newman she is right. With nothing to lose, she must operate outside the law one last time.