The Devil You Know is the 1125th episode of The Bill
P.C. Garfield and W.P.C. Keane attend a call about a disturbance outside a community hall where a birthday party is going on inside. When they put out the name of the suspect wanted for causing criminal damage, P.C. Quinnan recognises it as he has previously arrested the suspect for drug dealing and burglary. Quinnan and P.C. Slater pick him up and take him back to Sun Hill. He tells them he was there because of the birthday girl Amanda Ray. He had wanted her to go with him to another party but her boyfriend made her stay. He admits the charge of criminal damage, which he did to get back at her.
Later, Keane and Garfield find Amanda collapsed outside the hall from a suspected drug overdose. Her father blames the boyfriend for giving her the drugs and the boyfriend's father, a teacher at Canley comprehensive, for not supervising the party very well. Keane arrests the boyfriend at the hospital for possession of cannabis. He talks to Garfield off the record and the truth about who bought the drugs emerges.