“You cannot interrupt the signal without warning. The impulses within will disconnect and become deranged,” shrieks Sister Monica Joan (Judy Parfitt) as Sister Ursula (Dame Harriet Walter) switches off her beloved television set in the opening minutes of Call The Midwife’s series six opener.

And it seems as though her words are prophetic with regard to what’s about to unfold as the South Africa team return to London to discover there’s a new head of household.

Patsy and Delia – who have been living under Sister Ursula’s rule while the team were on their mission – can’t wait to see the back of her, but as the reunited friends (bar Helen George's Trixie who’s stayed on in South Africa’s Hope Clinic for now) sit down to a rather sparse lunch, there’s a telephone call that brings some very bad news.

The Mother House has overlooked Sister Julienne and it’s Sister Ursula who’ll be filling the void left by Sister Evangelina’s death.

And she’s taking great pride in lording it over the kind and caring Julienne, who’s forced to smile and offer her congratulations to the woman who’s taken her rightful place.

Ursula wastes no time in bringing in a new appointments system (which Doctor Turner likens to raffle), taking away Sister Monica Joan’s beloved television, stemming the supply of biscuits ("eating for two should be about careful nutrition, not self-indulgence”, she smiles) and charging Julienne with the heavy lifting – because nothing says “don’t get any ideas” like forcing the woman who was basically your equal to do the most menial tasks.

But office politics plays second fiddle to midwifery in Poplar and there’s little time for sniping as a new patient presents. Trudy Watts is heavily pregnant and struggling to get her son Mickey back to school.

He’s got an eye patch and is being bullied but she can’t cope with battling hospital waiting lists on the day her husband’s due for release from prison. 

It’s not long before we learn Lester – who’s fittingly won prizes for boxing while doing time – is good with his fists and has plans to send Mickey into the ring. Trudy’s not keen and gets no support at home, especially not from her mother, Zelda, who is Poplar’s very own Peggy Mitchell.

When his wife pulls Mickey from the boxing club and won’t give him what he wants Lester takes matters into his own hands, beating her, burning her with a cigarette, and locking her in their bedroom before she goes into labour.

It’s only when Trudy rushes to Nonnatus and is almost turned away by Sister Ursula that Sister Julienne finally bites the bullet, refusing to accept her new superior’s orders and delivering a baby girl on the clinical room floor.

It’s a bold but brilliant move from the nun, who’s put up with more than enough of Sister Ursula’s guff. Of course, her rebellion doesn’t go unpunished and her superior reprimands her the morning after the night before. 

Julienne isn’t the only one suffering under Ursula’s iron rule, though. Sister Mary Cynthia, who’s understandably still fragile following that horrific attack in series five, is struggling with the increased spiritual workload.

And when she witnesses the domestic violence Trudy’s been exposed to on a home visit the young nun finally cracks in a heartbreaking exchange with her fellow sisters. Doctor Turner is called and he prescribes a visit to a sensitive mental health community near her family home in Birmingham, but before he can do anything Sister Ursula ships Mary Cynthia off to the mother house without a word of warning. 

The incident at the Watts house leaves young mum Trudy shaken too. She attempts to divorce her husband only to be called a liar by her mother and have her dirty laundry aired. Trudy struggled when Mickey was born and put her head in the oven, and her family won’t be long using her past against her. Struggling to cope with the mental strain, she leaves the kids at the police station and makes a break for it – but it’s not long before Nurse Crane finds her and offers to help. 

Amid all the drama, Barbara’s been dealing with her own struggles. Vicar Tom can’t afford an engagement ring so the thoroughly modern Millie decides to do the shopping for him, meaning the pair can finally bring about an end to their friends’ eternal yapping about the blade of grass in the germaline tin.

Of course that’s nothing compared with her battle with a particularly violent potter’s wheel, granted. 

And there's some very good news for Shelagh Turner, who discovers she's pregnant despite an infertility diagnosis.

All’s well that ends well at the Commonwealth Day party, but there is a sting in the episode’s tail for poor old Patsy. Her father’s dying in Hong Kong – will she go to see him?