Five years ago, school girl Andrea "Andie" Bell was allegedly murdered by her boyfriend, Salil "Sal" Singh, who then killed himself. The case has now gone cold, but 17-year-old Pippa "Pip" Fitz-Amobi is convinced that the real killer is still at large. She starts a project (an EPQ in the British version) pretending to investigate media involvement in the case while actually trying to figure out who the real killer was, assisted by Sal's younger brother Ravi. She first suspects Max Hastings, a graduate known for starting calamity parties. They end up interviewing several people in and around the fictional town of Little Kilton, near London, which in the American edition is replaced by the equally fictional Fairview, Connecticut. They eventually discover what really happened: Andie hit her head during an argument with her secret lover, Elliot Ward. She then returned home and fought with her sister Becca, during which she fell and choked to death on her own vomit. Becca, angry with Andie, chose to allow her sister to die and hid her body. When Andie was reported missing, Elliot panicked and thought he had killed her and lured Sal into the woods and murdered him to cover up his involvement.