Former Sun Hill PC Diane Noble, now a Sergeant, joins Sun Hill for a night before joining her new post at Barton Street. She and Smithy lead the troops to a rooftop party at a building site, but events take a sinister twist when a boy falls from a ledge whilst high on ecstasy. Tests at hospital reveal they were mis-labelled as ketamine. Backed by Turner and Fletcher, uniform go undercover at a club to snare the dealer, with Taylor keen to impress Noble after getting off on the wrong foot. As Noble prepares to bow out of Sun Hill for one last time, she is called back to St. Hugh's when the overdose victim's father stands on the roof in a bid to commit suicide.