Christmas promises to be a memorable one at Nonnatus House as Lucille and Cyril prepare for their upcoming winter wedding. The Nonnatus team are faced with their busiest Christmas Day ever as the Maternity Home is filled with expectant mums-to-be, each with their own challenging case. Luckily Mother Mildred is on hand to support the team.

Demolition work in Poplar uncovers a long-buried secret that leads to a testing and emotional case for the team. Sister Julienne takes on a sensitive delivery.

At the monthly cytology clinic, Sister Frances comforts a young woman who is struggling with a life-changing diagnosis. Lucille supports a difficult mother.

Shelagh organises a special celebration to mark 100 years since the Order first arrived in Poplar - although Sister Hilda feels that she should have been in charge of the festivities. Nancy tackles the plight of meths drinkers living rough in Poplar, and Nurse Crane treats a young singer who is torn between two very different futures.

Sister Hilda and Dr Turner support a young father with a lung condition whose wife is planning a home birth, and discover he is also coping with the repercussions of a past trauma. Cyril looks for a job that will put his qualifications to good use, a first-time mother struggles to bond with her daughter, and Fred comes up with a way to keep the wards cool during a summer heatwave.

Trixie has been assigned to a complicated case involving a crane driver who was injured in a workplace accident and is now paraplegic. Meanwhile, Nancy and Sister Frances give a talk on the facts of life at a primary school, and Lucille's attendance at a straightforward delivery takes a distressing turn. Shelagh decides to organise a jumble sale to raise money to fix some broken playground equipment in the park. When Sister Julienne finds a suspicious item, chaos ensue

Sister Monica Joan seeks advice from a clairvoyant. Matthew is shocked to discover squatters in one of his warehouses, and Shelagh faces the most challenging delivery of her career.

Nonnatus House suffers its biggest threat yet. But this time it’s not the bricks and mortar that are in danger, it’s the people.

Nonnatus House faces its darkest day after a tragic incident in the heart of Poplar. As the community rallies together, the team must overcome personal anguish to help the injured.