As spring arrives, Nonnatus House welcomes two new nuns, the experienced Sister Hilda and newly qualified Sister Frances, who must acclimatise to the changing East End. A complicated multiple birth tests the skills of some of the midwives to the limit, but Trixie has to face her fears and Valerie deals with a shocking case that arrives unexpectedly.
Lucille treats an elderly hoarder suffering from a malodorous leg ulcer, and fears that living surrounded by towering piles of rubbish, books and tins of food will have a serious effect on her recovery. Sister Hilda has a challenging case on her hands when a family newly arrived from Ghana are found to be suffering from an unidentified illness, and Violet runs for a place on the local council, but Fred is not convinced she can make a difference to the community, placing more faith in the Civil Defence Corps.
Valerie helps a mother of five come to terms with her latest child's birth defect. The Turners oversee a measles vaccination trial at the clinic, but are concerned by an overly anxious first-time mother. They soon discover she is concealing a devastating loss, which could have serious repercussions. Nurse Crane decides to bring a taste of the seaside to Poplar for the Whitsun bank holiday, and Violet's political career goes from strength to strength as she wins the seat on the council for Poplar North.
Sister Julienne is drawn into a conflict between an estranged mother and daughter, both of whom are pregnant. Nurse Crane visits a photographic gallery in Soho with Sgt Woolf, but the trip does not go to plan, and Sister Frances' shyness causes concern. Trixie's keep fit class is chosen to host a special event, but her star pupil is devastated to learn that 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 to Nonnatus while Nurse Crane is in hospital receiving treatment for her back. With help from Trixie, she provides care for a retired dock worker whose former job has taken its toll on his health, only to discover his son may be suffering from a more severe condition. However, her insensitive manner angers the family and they refuse to let her help them.
Sister Frances panics when Mother Mildred insists that she attend her first solo birth before Nurse Crane returns, and Trixie treats a pregnant woman who discovers that she has gonorrhoea, a condition that could have serious implications for the health of her baby. The Turners try to persuade Violet to approve the formation of a Brook Advisory Centre, and Lucille looks forward to a second date with Cyril.
Shelagh organises a ballroom dance to raise money for the maternity home, in the hope of taking her mind off May's impending adoption. A terminally ill patient laments that she will not get the chance to dance one last time, but Sister Hilda is determined to make sure she does. Fred suffers an embarrassing condition, and cannot bring himself to see Dr Turner, while Nurse Crane is discharged from hospital and tries to play matchmaker between Sgt Woolf and Miss Higgins. Valerie and Trixie are called to testify in a court case.