Guest Stars Clare Calbraith as DC Rebecca "Shep" Shepherd Matilda Ziegler as Mary Culvert Rebecca Benson as Ruthie Culvert Maureen Beattie as Dr. Vivienne Ripman Kenneth Colley as Ronald Devreux Rita Davies as Sister Benedict Co Starring Riley Jones as DC Mark Edwards Jodie Comer as Izzy Rawlins Pippa Bennett-Warner as Sister Claire Darragh Horgan as Gideon Frane Oliver Edgar as Isaac Culvert Luke Edgar as Ruben Culvert Simon Banks as Cafe Owner Mark Quartley as Jamie Levinson Curtis Flowers as Jim McKinnon Ben Addis as David Gilloway Kevin Trainor as Kit O'Dowd