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.

Prasad claims that Dryden wanted Tommy silenced as he was blackmailing him about Carly, hence the ambush. However the order was to spare Lindsay. Hastings charges Dryden for the driving scam but has insufficient evidence for the weightier charges as Dryden apparently proves that the last he saw of Carly was when he put her on a train. Kate is surprised that Steve seems to believe in Lindsay's innocence until he admits that he is purposely trying to gain her confidence to trap her. When she is shown to have accepted a proposal by a colleague to snare a child abuser she seems less innocent than she claims but is she really guilty of conspiracy to murder?