There's a new face at Nonnatus House as Call The Midwife returns for a sixth series, but while Dame Harriet Walter is a welcome addition to the cast, Sister Ursula isn't quite so warmly received at the maternity home.

The new nun joins the ranks after the sad passing of the beloved Sister Evangelina, played by Pam Ferris, and dashes any hopes Sister Julienne (Jenny Agutter) had of leading the team.

"It’s back to earth with a bump for our beloved midwives as they return from their magical Christmas mission trip to South Africa. It is now 1962, and in a rapidly changing world, the arrival of Sister Ursula – superbly played by Dame Harriet Walter – brings new challenges to Nonnatus House," writer Heidi Thomas tells RadioTimes.com.

"Tears are shed, and bonds reinforced, as the team pull together as never before."

And they'll certainly need to do just that if they're to survive under Sister Ursula's new regime.