The story follows a group of new recruits in the Northern Ireland police force, serving their probation period under the guidance of seasoned mentors before joining active duty. At the heart of the narrative is 40-year-old single mother Grace Ellis, a former social worker from England determined to rebuild her life. Alongside her are the impulsive yet awkward Annie Conlon and the timid Tommy Foster, whose marksmanship leaves much to be desired. Together, they face the challenges and constant dangers of policing the turbulent streets of Belfast.