Christmas is coming, and in Poplar the midwives of Nonnatus House are busier than ever. When an abandoned baby is discovered on the steps of the convent, the whole community rallies round to provide food and clothing, and to try and trace his mother. Meanwhile, Jenny Lee finds herself drawn into the mystery surrounding elderly local woman Mrs. Jenkins, while Chummy is determined to stage an unforgettable nativity play.

Jenny celebrates her birthday with Chummy and the girls, but soon after finds herself taking care of a patient in an abusive marriage.

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 seconded to a short-staffed hospital in London, but grows increasingly reluctant to carry out her duties when she finds out she is working under intimidating surgeon Mr Tracey. Back in Poplar, the midwives are introduced to newcomer Jane and outspoken twins Meg and Mave Carter. The sisters are identical in every way, except one of them is now pregnant - forcing them to come to terms with the impact a baby will have on them.

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.

Cynthia has to administer daily insulin injections to diabetic John Lacey, a bully who consistently belittles his wife Annie. When Annie’s beloved son Bob pays a visit, Annie gains the confidence to start to turn her life around. Jenny looks after a black mother to be, Monique, who is subjected to racial prejudice from her neighbours.

The convent comes under threat of demolition. Fred's pregnant daughter and her young son come and stay with him. Jenny is wooed by a new love interest. Chummy and PC Noakes prepare for the arrival of their baby.