After a bungled raid which kills an innocent man young DS Steve Arnott faces disgrace. However he is transferred to the anti-corruption squad, whose head, superintendent Ted Hastings, gives him a "very special case" to investigate - DCI Tony Gates, recently awarded a medal for heroic conduct but with a suspiciously high arrest rate. Hastings tries to get Gates on minor bribery charges, in vain, and is unaware that the married Gates has covered up a fatal hit-and-run by his lover, businesswoman Jackie Laverty. Meanwhile DC Kate Fleming joins Gates's team and tells Steve she is investigating him from the inside following the deaths of two drug dealers.

Having been duped into covering up Jackie's hit and run, 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.

Gates, knocked unconscious by the attackers, tampers with evidence, hiding a whiskey glass before police arrive to find Jackie has vanished. He claims he has just got there himself. Hastings and Arnott quiz him on his relationship with Jackie and he admits she was an old flame but denies knowledge of her money laundering. Arnott goes over the top in confronting him with evidence to suggest he was at Jackie's house when she was killed but makes himself look desperate. Gates is taken off the case and later, whilst investigating Wes's murder, is grabbed by masked men and an evil child who threaten to frame him for Jackie's murder unless he takes over her money laundering racket.

A police convoy escorting a civilian under a witness protection scheme is attacked, the witness hospitalized and all the police officers killed, except Inspector Lindsay Denton, who organized the operation at very short notice and who only informed DCC Dryden of the route. Ted Hastings asks Steve and Kate to interview her but Kate pulls out, claiming one of the dead officers, Jayne Akers, was a friend - though she has been having an affair with Jayne's husband Rich. Her place is taken by Georgia Trotman, who is troubled that the men are savage with their interrogation, treating Lindsay as a suspect and delving into her finances. Lindsay herself is moved to a missing persons unit but is shown to have a violent streak, attacking a noisy neighbour. Kate follows her to the retirement home where her mother lives and finds she has rung the hospital from a payphone. Georgia and Steve attend at the hospital where somebody is trying to kill the witness and who kills Georgia.

AC-12's future hangs in the balance after Hilton bars them from investigating Roz Huntley. But Roz's problems are building closer to home.

Having been duped into covering up Jackie's hit and run, 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.

After a bungled raid which kills an innocent man young DS Steve Arnott faces disgrace. However he is transferred to the anti-corruption squad, whose head, superintendent Ted Hastings, gives him a "very special case" to investigate - DCI Tony Gates, recently awarded a medal for heroic conduct but with a suspiciously high arrest rate. Hastings tries to get Gates on minor bribery charges, in vain, and is unaware that the married Gates has covered up a fatal hit-and-run by his lover, businesswoman Jackie Laverty. Meanwhile DC Kate Fleming joins Gates's team and tells Steve she is investigating him from the inside following the deaths of two drug dealers.

Gates, knocked unconscious by the attackers, tampers with evidence, hiding a whiskey glass before police arrive to find Jackie has vanished. He claims he has just got there himself. Hastings and Arnott quiz him on his relationship with Jackie and he admits she was an old flame but denies knowledge of her money laundering. Arnott goes over the top in confronting him with evidence to suggest he was at Jackie's house when she was killed but makes himself look desperate. Gates is taken off the case and later, whilst investigating Wes's murder, is grabbed by masked men and an evil child who threaten to frame him for Jackie's murder unless he takes over her money laundering racket.

AC-12's future hangs in the balance after Hilton bars them from investigating Roz Huntley. But Roz's problems are building closer to home.

A police convoy escorting a civilian under a witness protection scheme is attacked, the witness hospitalized and all the police officers killed, except Inspector Lindsay Denton, who organized the operation at very short notice and who only informed DCC Dryden of the route. Ted Hastings asks Steve and Kate to interview her but Kate pulls out, claiming one of the dead officers, Jayne Akers, was a friend - though she has been having an affair with Jayne's husband Rich. Her place is taken by Georgia Trotman, who is troubled that the men are savage with their interrogation, treating Lindsay as a suspect and delving into her finances. Lindsay herself is moved to a missing persons unit but is shown to have a violent streak, attacking a noisy neighbour. Kate follows her to the retirement home where her mother lives and finds she has rung the hospital from a payphone. Georgia and Steve attend at the hospital where somebody is trying to kill the witness and who kills Georgia.