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.