This opening episode sees newly qualified midwife, Jenny Lee, arriving at Nonnatus House. Believing she has been sent to a small private hospital, Jenny is surprised to find herself at a convent. Initially daunted by her surroundings, and not least the formidable Sister Evangelina and the eccentric Sister Monica Joan, Jenny gradually begins to find her feet.

The story of the week focuses on the first case Jenny is allowed to handle alone, under the guidance of Sister Julienne – the care of Conchita Warren during her 25th pregnancy.

Conchita is married to Len, who fought in the Spanish Civil War and brought Conchita home with him. Conchita speaks no English and spends her days caring for her enormous family. Her case appears to be routine but, when freezing smog descends on London, events take a turn for the worse. Conchita slips and goes into labour at 30 weeks’ gestation, suffering from severe concussion.

Jenny, alone in the house with Conchita and her husband, must draw on all her reserves of skill and courage if Conchita and her premature child are to survive.

We also meet Pearl, whose indomitable spirit rises above a dose of venereal disease, and Muriel, whose home delivery shows the best and worst that the system has to offer.