Blue Lights Season 3 start date, cast, episode count and plot as it returns to BBCThe police drama starring Sian Brooke, Katherine Devlin and Nathan Braniff is back for a third runBlue Lights' Katherine Devlin discusses her characterBlue Lights is back for a third series, with the BBC promising "more high-stakes, gripping moments than ever before". ‌View 3 Images Katherine Devlin plays Annie in Blue Lights (Image: BBC)Blue Lights stars tease what to expect from their characters ahead of series 3 READ MORE:When is Blue Lights on? Blue Lights series three picks up with response officers Grace, Annie and Tommy, who are now two years into their jobs. The new batch of episodes will see them challenged as their work takes them into an underworld where accountants and lawyers facilitate organised crime. Blue Lights series three is on BBC One and iPlayer from 9pm on Monday September 29.