Nonnatus House is alive with preparations for Christmas. Chummy is arranging a nativity play with the Cub Scouts, Jenny is faced with a difficult case, and a young girl's predicament leads to a big decision.

        

Jenny tries to help a battered wife, Doctor Turner finds himself overcome with requests for nitrous oxide from pregnant women throughout Poplar, while Trixie and Sister Evangelia help deliver a baby in very unsavory circumstances.

           

Chummy makes an important decision, Jenny reconnects with Jimmy, and Cynthia's conduct is called into question after the death of a baby she delivered.

            

Jenny is sent to the London hospital as a surgical nurse and finds that her friend Jimmy is a patient. He's going ahead with his wedding plans and the surgeon, Aubrey Tracey, diagnoses his abdominal pain as premarital jitters and sends him home. Jennifer's first encounter with Aubrey in the operating theatre is unpleasant and the imperious surgeon gives her short shrift. When Jimmy, who was misdiagnosed, returns for an emergency appendectomy she realizes Tracey is making errors. Jimmy survives but Jenny feels compelled to do something. Cynthia works with identical twins Meg and Maeve Carter, one of whom is pregnant, though the staff have some difficulty telling them apart. The women are very dependent of one another and skeptical about medical care in general. Maeve, the pregnant one, seeks help over her sister's objections. The shy and somewhat nervous Jane Sutton, a medical orderly, arrives at Nonnatus House.

            

A friend of Chummy's, Reverend Applebee-Thornton, comes to stay at Nonnatus House and soon gets on everyone's nerves. Meanwhile, Jenny and Sister Evangelina deliver a baby with spina bifida, and Sister Bernadette plays matchmaker.

            

Nonnatus House prepares for the annual summer fête, but when a baby show is announced, the girls must find a host for the proceedings. Meanwhile, a patient of Jenny's puts her life at risk, and Sister Bernadette remains troubled.

            

Doctor Turner is concerned by the spread of tuberculosis in the community, Jenny tries to repair a father and daughter's fractured relationship, and Sister Bernadette receives devastating news.

            

Jenny encounters racism firsthand when assigned a Jamaican patient, while Cynthia has to deal with a cantankerous man suffering from diabetes. Sister Bernadette avoids Doctor Turner, and a familiar face returns to Nonnatus House.

            

Sister Bernadette is discharged from hospital, while a heavily pregnant Chummy resumes her midwifery duties. Jenny meets a new love interest, Fred's pregnant daughter pays him a visit, and Nonnatus House itself is under threat.