Christmas is just around the corner and the nuns and midwives of Nonnatus House are busier than usual. After an abandoned baby is found on the steps of the convent, the whole community comes together to offer food and clothing and attempt to locate his mother. Jenny Lee ends up getting caught up in a mystery that surrounds an elderly local woman called Mrs Jenkins. Chummy attempts to pull out all the stops to stage a memorable children's nativity play.

It is Christmas Eve, 1892, and the falling snow is the stuff of fairytales. But the fairytale becomes a nightmare, and a chilling menace threatens Earth.

The family receive a warm welcome at Duneagle Castle when they visit Rose and her parents in the Highlands. But there is no disguising the tensions between their hosts. Back at Downton, Carson is determined to keep the servants working hard, but with a country fair coming up, will some be tempted to push their luck? Could romance be on the cards for Mrs Patmore?

Dr. Hope Martin returns to ask Maura for a life-altering favor. Jane worries about the impending spinal surgery for Lt. Col. Casey Jones, and Tommy shows off baby T.J. But all gets shoved to the side when a building collapses, trapping loved ones inside.