It’s Christmas in Poplar, but the festivities are put on hold for several Call the Midwife favourites when disaster strikes.

In the festive special, the mother house in Hong Kong – filmed on location – collapses, leaving multiple casualties, including several children. But with few hands and limited supplies to manage the fallout, Nonnatus House steps in to help.

“We discover the ground underneath the mission has made it collapse,” explained Jenny Agutter, who plays Sister Julienne. “It’s just sunk away. Some people have died, the whole place is destroyed, and the orphans and mothers have nowhere to go.

“So, they get a small party together to go out to Hong Kong to see what they can do to help, try and find new premises and take care of things.”

Also joining them is Sister Hilda (Fenella Woolgar), “and that’s lovely,” said Agutter. “Although it’s difficult under the circumstances, there’s an excitement in being able to make a difference – and an energy that comes from working in a place where people really need you.”

“That stays with Sister Julienne. So, when she returns to the UK, it’s what she’s kind of hankering for.”

Fenella Woolgar as Sister Hilda, Patra Au as Mrs Ma and Jenny Agutter as Sister Julienne in the Call the Midwife Christmas special. BBC/Neal Street Productions /Charmaine Man
She went on to say that the theme of the special, which will have two parts for the second year in a row, is “unsteady ground”.

“Everything is about people being displaced in some way and the changes bringing something new and fresh,” she said. “But in other ways, it’s very disturbing.”

Also accompanying Sister Julienne and the others to Hong Kong is Sister Veronica, for whom the trip stirs up complicated emotions.

“She and Nurse Crane find a newborn baby who’s been left in a cardboard box, literally hours after being born,” said Rebecca Gethings. “It’s all looking quite bleak, but then the mother comes to collect the baby, so that’s a really lovely moment, but tough for Sister Veronica.

“She has bonded with this baby. She’s got these mixed feelings of delight that this baby’s going to be okay and reunited with his mother, but also this illogical wanting of the baby herself.”

Rebecca Gethings as Sister Veronica in the Call the Midwife Christmas special. BBC/Neal Street Productions /Charmaine Man
Gethings said that even though having a baby was “not on the table” for Sister Veronica, as a nun, she’s still “feeling the end of an opportunity to become a mother”.

“It’s a physiological pull that she’s going through, as she’s always in close quarters with babies,” she added. “It’s a story that will continue throughout the series. You’ll see that need grow in her.”

But it’s not just the Hong Kong crew who are put through their paces – the instability Agutter spoke of is also felt back in Poplar.

“They’re dealing with a family who are completely displaced,” she explained. “They are travellers who have no home, and who are having a child.”

Molly Vevers, who plays Nonnatus House’s newest addition Sister Catherine, expanded on that storyline.

“She gets involved in a case with two mums-to-be who are Irish travellers and living in a camp there,” she said. “As the story unfolds, there’s a lovely character called Queenie, who has a heartbreaking back story.

“And Sister Catherine is pivotal in supporting her and helping her process the grief she’s been through. It’s a really heart-rending story but woven in with all the Christmas magic of the rest of the episode.”