S12, E1: Leo is stopped for drink driving and finds himself having to do community service in a rough part of South London. When one of the lads is stabbed near their playing fields, Leo steps in and saves the boy's life. Elsewhere in South London, Nikki is called out to a funfair where a teenage girl, Shana, has fallen from a ride and died. Upon closer inspection Nikki suspects that the girl may have already been bleeding from a stab wound when she was strapped into the ride. DS Wallace, the investigating officer, suspects Shana may have been part of a gang and is the latest casualty in a turf war.