Boxing Day brings a large snowfall that covers the country. The adverse weather causes major disruption across Poplar as roads become blocked and pipes freeze. The milk float struggles to make its deliveries and families must queue outside for water from standpipes. Trixie's holiday with Christopher is cancelled due to the snow. Valerie helps Linda and Selwyn, an unmarried couple living in a caravan, prepare for their baby. As the labour progresses, unforeseen complications knock Valerie's confidence in her ability as a midwife.
Elsewhere, the freezing weather takes the life of Dr Turner's patient, Percy Tillerson. Sister Julienne must inform the family of his death and uncovers an uncomfortable truth about the chirpy late Percy.
Tom is offered a new position in Birmingham, but it would mean him and Barbara leaving Poplar for at least six months. It's all hands on deck to help during the weather crisis, so Shelagh comes back to work. Nurse Crane meets her match in Sergeant Woolf as he challenges her driving ability and Akela leadership. Proving him wrong, Nurse Crane is instrumental in bringing the milk float back to Poplar.