Nancy is a detective sergeant who hides a longstanding loyalty to a haulier and drugs trafficker named Frank. When a clandestine meeting ends in murder and Nancy is caught in the crossfire, her link to Frank suddenly risks being exposed. Seconded to the murder investigation in her home town of Brighton, she finds herself playing a very dangerous game, as under the gaze of her new colleagues, Nancy must track down the killer while all the time concealing her role as the missing witness. When someone connected to the investigation is attacked and a vital piece of evidence goes astray, Nancy realises with horror that the killer is close, and may be getting inside help from the police.
A wounded and mistrustful Nancy desperately needs an ally - but she cannot open up to Hayley for fear of putting them both in danger. When the police make a public appeal hoping to find the missing witness, Nancy is unexpectedly forced into the spotlight, which also brings an old enemy out of the woodwork. Soon after Nancy receives a package, and she realises that someone is on to her. She warns DS Kevin O'Dowd that there is a leak on the team, but cannot say more for fear of exposure. Meanwhile, the murder investigation focuses on Frank Le Saux's accountant, Theo Kettler. When a witness links Theo to a Newhaven garage suspected of drugs trafficking, the police mount a surveillance operation. Pursuing her own dangerous investigation, Nancy finds herself at the same location - only to stumble into a second shocking murder.
In the wake of the latest killing, suspicion shifts to garage owner and Le Saux associate Duncan Elliot. Visiting Elliot, Nancy spots Theo Kettler's missing car. A vital piece of evidence is recovered from the car, giving DCI Newman a breakthrough but placing Nancy in even greater danger.
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.
Stood down by Newman for being too emotionally involved, Nancy is forced to operate outside the law to prove her case against Nash.
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.
