The four courageous Bletchley Park girls continue to help England win World War Two at the top secret code-breaking centre where they work. The fourth Christmas of the war is approaching fast. It should be a happy time yet life throws them challenges they could never have imagined. Lily's heart is torn in two when her boyfriend Grant is badly injured in an air raid. As he spirals into despair she must find a way to give him hope again. Bronwyn has a new romance on the horizon. But will the widower's young daughter accept her or will she jeopardise Bronwyn's hopes for love? Peggy is terrified her secret will be disclosed when she has to look after her sister's daughter. Can she escape the shame of her past? Caroline has had a sheltered privileged upbringing. Will her natural confidence be shattered when she learns about her boyfriend's hidden life? Despite rationing heartache and the endless war the Bletchley Park girls prepare for an unforgettable Christmas.