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.

Following the deaths of Georgia and the witness it is Steve who gets a grilling as to the police presence at the hospital whilst Lindsay is accused of attacking her neighbour, which she denies. Steve discovers that a nurse on the witness's ward, Claire Tindall, was threatened into giving the killer access by a man she knows as Joe, but whom she is unable to identify. Lindsay continues to search for vanished teenager Carly Kirk and Kate is drafted in as her assistant - in reality a move to try and get Lindsay to admit her guilt - but Lindsay sees through the ruse. After Kate's cover is blown Lindsay is questioned again and claims that she rang the hospital to ask that the witness exonerate her but she is disbelieved and Hastings arrests her for conspiracy. At her interview she points out that Steve visited Claire unofficially and Hastings has financial problems and a broken marriage that could make him just as culpable but she is nonetheless held in custody. Meanwhile DCC Dryden finds himself in the frame for a driving offence supposedly committed by his wife.

An arrogant Dryden is questioned regarding the traffic offence and is dismissive though Steve lets him know Lindsay has revealed that he knew about the convoy route and aims to pursue it further. Rich Akers is also pulled in after £20,000 of which he claims ignorance is found under the floor boards at his house. Hargreaves is convinced this was the bribe given Jayne to betray the escort and when Steve and Kate examine Jayne's car they discover a tracking device though Hargreaves is not keen for its revelation. Furthermore Cottan and Hargreaves see video evidence suggesting that Tommy had a grievance against Dryden, whose affair with Lindsay is now proved. Lindsay gets a day release from prison to visit her mother, in hospital after a stroke, but on the way back the prison van is hi-jacked and she is abducted by two policemen, Prasad, identified by Carly's parents as her apparent boyfriend, and Cole.

Lindsay wakes up in a lock-up and is questioned by her abductors. Prasad soon kills his accomplice, Cole, but Lindsay outwits him and makes him admit on the phone that he and Cole were working for Dryden, who set up the ambush. Steve locates her at her dead mother's bedside and she is granted bail, unaware that Prasad, whom she believed that she killed in self-defense, is still alive and demanding immunity. Cottan brings in his old mate Morton for some dirt on Dryden and it is revealed that Dryden had sex with Carly Kirk. He is arrested and questioned, admitting that he had a brief affair with Lindsay, who became vindictive when he ended it. Steve also finds out that Lindsay has had an abortion.

A fresh police leak enables another audacious raid, while Arnott's attempts to gather information put him in a dangerous situation.

Corbett's most daring plan yet requires McQueen to exploit links with corrupt police officers. Meanwhile, the AC-12 team make a shocking discovery.

Tensions rise in the OCG following the events at Eastfield. With troubling questions hanging over the identity of the mysterious H, suspicions mount among the AC-12 team.