Life as a WAAF in wartime England is not as glamorous as Sylvia Bishop had anticipated, although in letters home she tries to keep up the pretence for her sister Daisy. Then she is posted to a new RAF station and her work becomes more interesting. She is put in the Photo Intelligence unit and becomes very good at her job. Frustratingly, she cannot tell Daisy or anyone else what that entails as she has had to sign the Official Secrets Act. Her secret job is not the only thing that inhibits Sylvia from confiding in her sister. She has fallen in love with handsome Wing Commander Hugh Smythe, a forbidden love as he is married. If their relationship is discovered it will mean scandal and ruined careers for both of them. Sylvia desperately tries to forget Hugh and concentrate on her very important work. But how can she when she works so closely with him?