Brother and sister Martin and Hilda Massie live together, leading a quiet, Christian existence in the confines of the Bluebell Hill Development. Just as they are preparing for a housewarming gathering, their peace is shattered by a young trespasser in their garden. The Massies' neighbours congregate in their living room and together they agree to form a neighbourhood watch group to safeguard against further incidents. But after the Massies' beloved garden gnome Monty is thrown through their window, matters swiftly escalate, complicated by Martin's burgeoning romance with Amy, wife of Gareth, who was formerly involved with Luther, husband of Magda. What begins as a well-intentioned scheme for a safer community ends in violence and acrimony.