A Confession is based on the true story of the disappearance of 22-year-old Sian O'Callaghan in March 2011. Set in Swindon, Wiltshire, Sian was on a night out with her friends when she decided to walk the 15 minutes home from Swindon Old Town. But after failing to arrive home or respond to increasingly frantic text messages from her boyfriend, Kevin Reape, she was reported missing.
The series follows Detective Superintendent Steve Fulcher's character, who deliberately breached police procedure to catch the killer. He believed Sian may have still been alive and was being held against her will, but it was this decision to break protocol that led to an unusable confession, and ultimately, ended his career and cost him his reputation.
As the investigation into Sian's disappearance is unfolding on the local news, and in the town, Karen Edwards — the mother of Becky Godden, a 20-year-old who disappeared in 2003 — is gripped with fear that her daughter will somehow be linked with this crime. Becky was a known drug addict and sex worker who had disappeared many time before but had not been seen in almost a decade.
A Confession portrays the intersection of Sian and Becky's families throughout the investigation as the detective narrows in on the chief suspect and local taxi driver Christopher Halliwell.