The body of a young girl is found naked and severely wounded on a patch of wasteground, leading Charlie to suspect the victim is Mandy Grainger, who parents reported her missing earlier in the day. When the victim is identified as male - Jez Collins, a post-op transgender - the team suspect that he may have been Mandy's boyfriend. With Mandy still missing, the team discover evidence which links both victims to a house party the previous night, but when Jack interviews homeowner Emily, she denies all knowledge of the pair. When it transpires that Mandy is also in the process of change from girl to boy, the focus of the investigation soon turns towards Mandy's father.