Guest Stars Kevin McNally as Professor Peter Cherry Kaye Wragg as Valerie Fullerton Emily Piggford as Professor Elizabeth Newport Maeve Courtier-Lilley as Vanessa Miller John Thomson as DI Warren Bull Diveen Henry as Elaine Robinson Ashley Margolis as Haidar Alam Richard Keep as Harrison Cairney Isobel Wood as Celeste Locke Julie Jupp as Woman with Dog Harry Lister Smith as Homeless Man James Craze as Roy