1958 is drawing to a close as the residents of Poplar prepare for Christmas. Festivities are thrown into chaos when an unexploded bomb is discovered close to Nonnatus House, causing mayhem among the nuns, midwives and residents of Poplar just days before Christmas. Everyone is evacuated from their homes, and the midwives of Nonnatus House are tasked with overseeing the rescue centre until the bomb is made safe. Jenny Lee finds herself drawn into the lives of young couple Yvonne and Alan Bridges, who are expecting their first child. Since fighting in the Korean War, Alan has suffered from post-traumatic stress disorder and Jenny, with the help of Trixie, becomes instrumental in helping him to overcome his fears. Elsewhere, Shelagh Mannion, formerly Sister Bernadette, and Dr Turner prepare for their understated wedding. But when Timothy is struck down with a potentially fatal illness, their plans are put on hold while they keep vigil at his bedside.