Trixie's feathers are ruffled when Jenny is promoted, but the new Acting Sister has more to worry about after a mother-to-be reveals the baby she is carrying doesn't belong to her husband - and to complicate matters, the real father is black. Cynthia is inspired by a lecture on natural childbirth, convinced it will help an overly anxious patient, while Alec and his friends try to persuade Jenny to join them on a CND march.

Sister Julienne receives an SOS from Holloway Prison, whose usual maternity workers have been struck down by illness, and when she and Trixie step in to help, the nun puts her reputation on the line to prevent a heavily pregnant convict having her unborn baby taken away by social services. Shelagh faces heartache when a routine pregnancy check reveals something far more serious, Alec has a confession for Jenny and Fred takes the gang to the theatre to celebrate Chummy's birthday - only for the trip to end in disaster.

Jenny has an eventful few days, starting with a patient who as well as having herself to worry about, is also struggling to cope with her mother, an agoraphobic who hasn't been outside for at least 12 years. On top of that, Alec asks the midwife to accompany him to Brighton for the weekend, leaving her wondering if his intentions are strictly honourable. However, things soon take a tragic turn. Meanwhile, Shelagh joins the local choir to take her mind off her problems.

Barbara faces her most challenging case to date when she treats first-time mother Abigail Bissette and the birth does not go according to plan. As Sister Julienne struggles with the increasing financial pressure on Nonnatus House, a mystery benefactor comes to the rescue. Elsewhere Sister Evangelina is unimpressed by newly arrived nurse Phyllis Crane.

The Nonnatus team rallies to support first-time parents Marie and Tony Amos when Tony is arrested for gross indecency with another male. Elsewhere, as Poplar is gripped by an outbreak of dysentery, Trixie undertakes her first official church duty since her engagement to Tom.