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.

Hesitant nursing assistant Jane Sutton arrives at the convent as Jenny is seconded to hospital work, meeting Jimmy, who, to her surprise, is one of the patients. Arrogant surgeon Aubrey Tracy misdiagnoses Jimmy and an operation is required, where Jenny acquits herself well. She also sees that Tracy is himself ill and he resigns. Meanwhile aggressive twins Meg and Maeve Carter - both married to the hen-pecked Sid - arrive at the clinic as Maeve is pregnant. However they eschew modern medicine for old herbal remedies and, following a bleak tarot card reading, the over-bearing Meg scares her sister into refusing hospital admission. Ultimately Maeve senses that she needs professional care and allows the midwives in for a home birth - where a new generation of twins is born.

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.