When 16-year-old Becky Watts went missing in 2015, it sparked a major police investigation and dominated headlines nationwide. Everyone was desperate to find the missing teenager. But only two people knew where she was – Becky’s stepbrother Nathan, and his girlfriend Shauna. Featuring incredible video footage and testimony from the police and Becky’s family, the documentary lifts the lid on the tactics that drove every step of this complex and tragic investigation and the 'cat and mouse' between the police and the suspects that played out in the interview room, and that caught the killers who thought they could get away with murder.