When a counterterrorism raid goes tragically wrong, DS Steve Arnott refuses to participate in a cover-up. Ostracised by colleagues, he transfers to an anti-corruption unit led by Supt. Ted Hastings. He soon finds his target is the city's top detective, DCI Tony Gates. with whom he must engage in a cat-and-mouse struggle to uncover Gates' secret.

Having been duped into covering up Jackie's crime, Gates is desperate to sever ties with her. But, as Arnott and Fleming close in on his secret, Gates is plunged into an even more dangerous situation than he first thought.

Arnott is convinced Gates played a part in Jackie's disappearance. With Fleming's help, the anti-corruption team tries to trap Gates into revealing his involvement in covering up Jackie's crimes.

Desperate for proof of Gates's corruption, Fleming pushes her relationship with him to the limit, but her behaviour causes Morton to question her loyalty.

With Gates on the run the anticorruption team find themselves under pressure to close the case. There is tension between Arnott, Fleming and Hastings, as Arnott questions how intimate Fleming was prepared to become with Gates. Gates still thinks that he can save his career and marriage. Arnott is forced to decide where his loyalties lie.