When a baby is born with severe deformities of the kind later identified as caused by the drug thalidomide, the midwives find it difficult to handle the situation, and the baby's father rejects her completely, to his wife's dismay. Trixie's new sideline as a keep fit instructor brings her into conflict with Sister Julienne, and she also becomes suspicious of the relationship between Barbara and Tom. Rather than return to Wales as her mother wishes, Delia moves into Nonnatus House.

Barbara treats a pregnant woman whose dockworker husband is struggling to support her as opportunities for work dry up. She is forced into a difficult decision that leaves Barbara facing the biggest test of her career. Nurse Crane meets a kindred spirit when she learns to speak Spanish, and Sister Evangelina helps a woman with breastfeeding, leading to unforeseen consequences.

A rare disease spreads around Poplar Street, and Patsy and Dr Turner try to trace the outbreak to its source. Suspicion over the identity of the first carrier threatens to divide a previously close-knit family. Sister Winifred is forced to confront her prejudices while treating a patient, and Barbara worries about how Trixie will react when she agrees to go to dinner with Tom.

Sister Julienne is seconded to a maternity ward, and is impressed by how modern technology is being used to help the mothers - but is left with a moral dilemma after assisting on a traumatic birth. A young man from Poplar is delighted to be accepted into university, but his mother is less than happy. His dreams are jeopardised when his girlfriend gets pregnant, a development that puts pressure on the whole family.

Turner and Shelagh are at the forefront of the advances in medical technology, and begin a campaign to ensure better respiratory health for their patients. However, Timothy fears their own lifestyle is not good for them and tries to encourage his parents to give up smoking. Violet injures her back and is forced to leave the shop in Fred's hands, a decision that strengthens their relationship but which proves to have other, unforeseen consequences. A new mother's past comes to light, with devastating repercussions for her family. Nurse Crane draws on her own experiences to help her.

Poplar is rocked by a series of violent attacks on women, and a prostitute is too ashamed to report what she knows - but her actions lead to a dangerous man roaming the streets, with devastating consequences for the residents of Nonnatus House. A mother tries to keep her daughter's pregnancy a secret to avoid gossip, putting her life in danger. The Turners go on a long overdue holiday, but the weather ruins their plans.

The introduction of the contraceptive pill is welcomed by Dr Turner, but some of his colleagues are less keen on the idea. Patsy tries to help a bargee who wants to give birth among her own community rather than in a maternity ward. Nurse Crane deals with an emergency during a storm, and a familiar face returns to Nonnatus House - but has been changed by her time away.

Dr Turner is horrified to realise he may be partly to blame as the cause of the recent rise in birth deformities comes to light, and tries to prevent further cases. Sister Evangelina returns to work, but has clearly been affected badly by her stroke, and her health continues to deteriorate. A pregnant bride goes into labour during her wedding reception, while her mother is forced to come to terms with her grandchild being conceived out of wedlock.