Sarah Lancashire returns in Sally Wainwright's acclaimed BBC thriller. Unsmiling police officer Catherine Cawood returns to lead her team in the Calder Valley, West Yorkshire. While on duty, she makes a horrific discovery - a dead body. The victim's injuries are strikingly similar to a string of murders in previous months, suggesting a serial killer is on the loose. But the case becomes even more shocking when it's revealed that Catherine knew the victims - something that could have serious implications for her and her family.