Boxing Day sees heavy snowfall covering the country and the adverse weather causes major disruption across Poplar as roads become blocked and pipes freeze meaning families have to queue outside for water from standpipes. Sister Julienne must inform a family about the death of their loved one and uncovers an uncomfortable truth, while Valerie helps an unmarried couple living in a caravan prepare for their baby, but unforeseen complications knock her confidence in her ability as a midwife. Guest starring Anita Dobson.

The winter continues, and the team at Nonnatus House welcome their newest midwife, Lucille Anderson. Nurse Crane and Dr Turner care for an elderly cancer patient facing eviction.

Lucille faces racism and prejudice when a new mother falls ill. Sister Winifred is keen to have fathers be more involved in the care of their babies.

The team must rally to prepare for Sister Monica Joan's birthday. Meanwhile, the closing of a nearby maternity home brings an influx of expectant mothers to the Nonnatus midwives.

Nonnatus House welcomes two new nuns. Valerie deals with a shocking case that arrives unexpectedly, and the other midwives must handle a complicated multiple birth.

Lucille helps elderly hoarder Clarice Millgrove who is struggling to keep her independence; Sister Hilda and the team work hard to help a Ghanaian family with an undiagnosed illness; Violet puts herself forward in the upcoming elections.

Valerie helps a struggling mother accept her son's birth defect. The Turners oversee a measles vaccination trial at the clinic as the team prepare for the Whitsun bank holiday.

The team tries to unite an estranged mother and daughter who are both pregnant. Trixie's friend is devastated to discover she is pregnant.

Poplar welcomes a brand new cervical cancer-screening clinic to the Institute and Dr Turner, Shelagh and Trixie are pleased to be part of the exciting new venture.

Mother Mildred returns and helps a docker family tackle end-stage pneumoconiosis. Lucille cares for an unmarried teenage mother who wants to keep her baby.

Mother Mildred decides it’s time for Sister Frances to attend her first solo birth. Trixie consoles a patient who discovers she has gonorrhea.

Sister Hilda digs deep to give her terminally-ill patient her final wish whilst the Turners must prepare to say goodbye to May. Fred and Reggie are keeping secrets from each other.