The Metropolitan Police Serious Crimes Squad sweep into Sun Hill and commandeer the station's briefing room, setting a few noses out of joint in the process. They are there to investigate the murder of a police informant, who at the time of his death was under the protection of Sun Hill CID. DI Burnside and DS Roach come to blows when Roach refuses to share the blame for withdrawing officers from the safe house, and accuses Burnside of corruption.