In Bolton, 15-year-old Reece Tansey is stabbed to death as Greater Manchester Police arrest two ordinary schoolboys on suspicion of murder. With no murder weapon and their refusal to comment, can social media data, revolutionary smartphone analysis and CCTV footage help police piece together what happened? Meanwhile, Lancashire Police discover the body of pensioner Bill Howard who appears to have been brutally tortured and then stabbed to death. In Accrington, Lancashire Detective Chief Inspector Al Davies has used phone records to zero in on a prime suspect.

Police are on the hunt for a suspected serial killer in Greater Manchester, and an online feud leads to a frenzied murder in Nelson in Lancashire. Smartphone and CCTV analysis might help find the suspect and solve the murder.