Peggy Thornton has always felt her middle-class life, living in Highgate Hill, to be rigid and narrow, so when women are urged to help on the home front after the outbreak of the Second World War, she starts training as a conductor on a London Transport bus. Her parents are appalled, but they're not the only ones who make her life difficult. Many of the bus crew haven't adjusted to women from their own class working let alone the likes of Peggy. And, her relationship with Leo, one of the depot's mechanics, serves to create further tensions. It is only when the real enemy strikes, and a German bomb explodes in the path of a bus, that these differences are cast aside but, for some, it may be to late...