It’s 1963 and Poplar is covered by a thick blanket of snow as the nuns and nurses of Nonnatus House face the challenge of the coldest winter for three hundred years. Battling against snow, ice, power cuts and frozen pipes, the midwives brave the elements to provide the best possible care for their patients. Valerie helps a young couple newly arrived in London, who experience a traumatic birth. Sister Julienne strives to reunite a family torn apart by a tormenting father.