The series tells the story of how Detective Superintendent Steve Fulcher, played by Martin Freeman (StartUp, The Hobbit, Sherlock, Fargo), deliberately breached police procedure and protocol to catch a killer, a decision that ultimately cost him his career and reputation.

Set in Swindon, Wiltshire, ‘A Confession’, details the disappearance of 22-year-old Sian O’Callaghan in March 2011. On a night out with girlfriends, Sian left a nightclub in Swindon Old Town to walk the 15 minutes home to boyfriend Kevin Reape, played by Charlie Cooper (This Country). Worried for her safety, Kevin reports Sian missing when she fails to come home in the early hours or respond to his increasingly frantic texts.

With the police investigation underway, officers arrive on the doorstep of Sian’s mother, Elaine Pickford, played by Siobhan Finneran (Cold Feet, The Moorside, Happy Valley), who at first thinks her daughter must have stayed overnight with a girlfriend. Described as a ‘family girl’, it was uncharacteristic of Sian to be out of touch with her loved ones.

Senior Investigating Officer Steve Fulcher leads a team which begins to piece together Sian’s last movements, scouring CCTV footage from the club and re-tracing her steps home. Cell-site analysis reveals her mobile phone signal bouncing off a mast 14 miles away in Savernake Forest. With the missing person’s enquiry in full swing Fulcher, orders a full-scale search operation.

Believing Sian may still be alive, Fulcher operates on the premise that Sian is being held somewhere against her will. If she is, he knows it will be a race against time. Through diligent and painstaking police work Fulcher and his team discovers CCTV footage of her in the High Street, which leads to vital clues in the investigation.

Meanwhile, Karen Edwards, played by Imelda Staunton (Maleficent, Paddington, Harry Potter, Vera Drake, The Girl), the mother of Becky Godden, a 20-year-old who disappeared a decade previously in 2003, is watching the investigation unfold on the local news and in the town centre. Reminded of Becky’s disappearance, she becomes gripped by fear that her daughter will somehow be involved in what is unfolding before her eyes as the search for Sian goes on.

A known drug addict and prostitute, Becky had disappeared many times before and although Karen had tried to help her daughter, staging interventions and paying for rehabilitation, sadly Becky continued to lapse back into addiction.

Coincidentally, the property where Karen lives with her second husband, Charlie, backs on to the home of Elaine Pickford and her then partner. Although they don’t know one another, their lives become tragically intertwined when Fulcher and his team edge closer to their chief suspect, local taxi driver Christopher Halliwell, played by Joe Absolom (Doc Martin, The Level, Suspects).

The investigation culminates in a standoff between Fulcher and Halliwell at a remote location, before Halliwell is taken back to the police station and given a solicitor. Just as Fulcher is about to give up, Halliwell suddenly makes a startling confession. But this moment of apparent triumph takes on sinister consequences and steers the investigation in a completely unforeseen direction.

ITV Studios Global Entertainment will distribute the drama internationally.