DCI Falcon and the team rally round to support forensic psychiatrist Fiona Nightingale after she is attacked by an unknown assailant in a manner frighteningly reminiscent of a previous attack. As they investigate further, the prime suspect is identified as Debbie Connelly - one of Fiona's former patients and a woman hell-bent on vengeance against the doctor who had her locked away. But Debbie's plan for revenge is far more elaborate than any of them realize and before long, Fiona is forced to go into hiding in 'the wasteland', on the run from both Debbie and the police. But Fiona cannot hide there for long and the homeless community are scared, fearing a character known only as The Shadow. As the full scale of the attack is discovered, Falcon and the team race to save Fiona from Debbie's final act of vengeance.