It's May 1970, and the Nonnatus team prepare for the arrival of a new nun and trainee midwife, Sister Catherine. Under Nurse Crane's supervision, Sister Catherine is thrown into a complex case. Dr Turner is taken aback when mother of seven Peggy Wrigley asks for an abortion. Although legal, the process isn't straightforward, and Dr Turner wants to ensure Peggy has thought this through. Meanwhile, Peggy's daughter Gail is expecting her first baby with a young RAF airman who is posted in Cyprus. Elsewhere, Dr Turner is disappointed by the general apathy towards the measles vaccination clinic as uptake remains relatively low despite the current high rate of cases.