Nurse Crane's back troubles return with a vengeance; Mother Mildred returns and helps a family tackle end-stage pneumoconiosis; Lucille cares for an unmarried teenage mother who wants to keep her baby.

Trixie cares for heavily pregnant Heather Pugh, who confides in Trixie that her waterworks are causing her pain. Routine tests reveal an unfortunate truth: Heather has gonorrhea, a sexually transmitted infection that could cause serious health concerns to her unborn child. Mother Mildred decides that inexperienced Sister Frances must attend her first solo birth before Nurse Crane returns, and Lucille gets ready for her second date with Cyril.

Sister Hilda digs deep to give a terminally-ill patient her final wish; the Turners prepare to say goodbye to May; Valerie and Trixie testify in court; Fred and Reggie keep secrets from each other.

As Christmas approaches, a bout of influenza sweeps through both Nonnatus House and the Turner family. When Mother Mildred declares that God is calling her to set up a branch house in the Outer Hebrides, it seems an ideal opportunity for the nuns and midwives to convalesce in the bracing Scottish air.

Dr. Turner, Shelagh, Mother Mildred, Trixie, Sister Julienne, Valerie and Lucille set off on their journey to the Outer Hebrides, where they are to stay in a freezing cold converted church. As the team set about establishing an antenatal clinic and treating the local population, they must battle not only the weather and bleak terrain, but the suspicions of some of the islanders.

Dr. Turner and Nurse Crane must deal with an alarming outbreak of diphtheria. Fred finds an abandoned baby in a dustbin, and the team must help locate its mother.

Fred and Sister Monica Joan catch a woman stealing milk, and end up caring for her when they find out she is pregnant; romance blooms between Miss Higgins and Sergeant Woolf.

Lucille is seconded to St. Cuthbert's where she delivers a baby in an elevator; Nurse Crane gives vaccines to new students; Violet, Trixie, Sister Frances and Valerie organize a fashion show for the community.

Four new doctors arrive at Nonnatus House, causing a stir among the midwives; Fred makes a discovery while on rounds.

Sister Frances is at a loss when she cares for diabetic and recovering cancer patient Albert Calthorpe, whose capable wife Grace refuses to accept further help despite having to care for her husband, her elderly mother, and a daughter who has a three-year-old and is about to have another baby. Nurse Crane and Sister Hilda become involved with an anxious new father, Ronald. Determined to be there for the birth of his first born, Ronald gets on Nurse Crane's nerves during the delivery. It is Sister Hilda who tactfully encourages Ronald to open up about his own childhood and get to the bottom of his motivations. Meanwhile, Violet is given two tickets to the new hit musical The Sound of Music, but as Fred is not interested in the film, Violet decides to raffle them off with all proceeds going to the incubator fund. Sister Monica Joan tries several times to win the tickets but is disappointed with each go. She soon concocts a plan to convince the skeptical Sister Julienne that perhaps a trip to the cinema might benefit the whole of Nonnatus House.

Fred attempts to reinstate the Poplar Horticulture Show; the Turners receive alarming news about their daughter; Valerie's pregnant cousin hopes her baby is born before her due date.