Police Constable Jo Gillespie (Sheridan Smith, The C Word, Accused) is devastated when her detective husband, Ryan, is shot dead in an abandoned warehouse. But her grief gives way to shock when she learns that Ryan was working undercover at the time of his murder. Jo struggles to remain strong for her family as she questions whether she ever really knew her husband. Although the police brass urge her to stay out of the investigation, Jo begins to doubt her fellow officers and searches for the killer with the help of her handsome colleague (Matthew McNulty, Jamaica Inn, The Paradise). As Ryan’s secrets come to light, Jo’s quest turns dangerous, and she fears she can’t trust even those closest to her.