A new regime begins at UCOS with the arrival of new boss DCI Sasha Miller. An unexploded World War II bomb is unearthed on an urban allotment in west London, dredging up a long-hidden murder weapon, and the team find themselves investigating a ritualistic killing of an Italian immigrant from 25 years ago. During the investigation, Gerry struggles to accept his new boss, and adamant that she is not pulling her weight, threatens to quit UCOS. Can Sasha earn the respect of UCOS's longest-serving officer by cracking the case?