In the spring of 1957 newly qualified midwife Jenny Lee arrives in the East End of London to begin her career. After overcoming the initial shock that her new home is a convent rather than a private hospital she quickly becomes immersed in her new life. Living with Nuns and working in a community of colorful characters is different from anything Jenny has encountered previously.

As Jenny Lee settles into her role, there is a new arrival at Nonnatus House, Chummy. A welcome pair of extra hands, Chummy sets about showing her worth, but an overwhelming keenness to please and her inability to ride a bike prove obstacles in gaining the respect of Sister Evangelina. Meanwhile a chance encounter with a young pregnant runaway forces Jenny to see an unfamiliar darker side of life.

Jenny is placed on the district nursing roster for a few weeks to extend her experience of community practice. At the antenatal clinic Trixie and Cynthia enroll a new patient. In her forties Winnie had thought her days of diapers and babies were long gone, and seems upset. By contrast her husband Ted is overjoyed by the news. However at the baby's birth everyone gets a bit of a surprise.

A baby girl is snatched from her carriage, causing great anguish to her family and uniting the local community as they search for the missing child. Meanwhile Cynthia witnesses another type of loss as she assists in the case of soon-to-be parents David and Margaret. Newly married and excited about their future, everything is put in jeopardy when Margaret develops eclampsia.

Jenny finds herself for once not involved in the beginning of life, but at its end. When Frank is diagnosed with cancer Jenny and the nuns are called upon to provide him with care. In doing so Jenny comes to know the siblings better, learning of their upbringing in a workhouse and the profound effect it has had on their relationship.

Sister Monica Joan is found wandering near the docks, and returned by the police. Her adventure takes its toll on her health and she succumbs to pneumonia. When she eventually recovers she sails forth back into the community only to find herself in trouble with the law when she is accused of theft. Chummy has further worries when her mother decides to make a trip to inspect her new "beau".