Sarah Lancashire has said working on the much-anticipated second series of Happy Valley was "emotionally brutal".
The 51-year-old Last Tango In Halifax star has returned to her Bafta-nominated role as formidable police sergeant Catherine Cawood.
BBC One's Yorkshire Valleys-set series gave Grantchester star James Norton his television breakthrough as psychotic Tommy Lee Royce.
Written by Last Tango In Halifax's Sally Wainwright, Happy Valley drew an impressive consolidated audience of 7.8 million for its series one finale in 2014.
The broadcaster and viewers wanted the story to continue, but Lancashire admitted she had to be convinced by Wainwright.
"I was nervous and wasn't sure whether we should be doing it," the ex-Coronation Street actress said.
She added: "But when I read them (the scripts), I thought - she's pulled it off."
The Corrie connection also sees former cast members Katherine Kelly, currently co-starring in ITV's Mr Selfridge, and Julie Hesmondhalgh, lately of Channel 4's Cucumber, join series two.
Dedication to her job masks Cawood's personal family tragedies: she believes Royce is responsible for her daughter's rape and eventual suicide.
Grandson Ryan (Rhys Connah) was conceived as a result of the assault.
The policewoman's marriage to Richard Cawood (portrayed by Derek Riddell) broke down and she is estranged from her son Daniel (Karl Davies).
As series two begins, Cawood's sister Clare (Downton Abbey's Siobhan Finneran) who was in recovery from heroin addiction, has fallen off the wagon.
Events have moved on by 18 months and Royce is in jail.
With little to do other than work-out, the imprisoned man's focus is on his nemesis.
The tense relationship between Cawood and Royce was a highlight of the first run, but the second will see a change due to Royce's circumstances.
"We meet face-to-face once," Lancashire revealed, calling Royce "an intrinsic factor" of Happy Valley's success.
"I can't see the show without him otherwise it's a cop show," she said.
"What sets this piece apart is that it should always be a good psychological piece of drama. They've ramped that up hellishly this series."
Lancashire, who revealed she was "very, very surprised" at the acclaim and popularity for Happy Valley, described working on the show in 2014 as "brutal".
"It's emotionally brutal again," she said. "The whole thing is draining simply because of her disposition, because she wears her emotional state of mind everywhere.
"She carries it around with her all the time."
The first series contained disturbing scenes, in particular a bloody fight between Cawood and Royce which sparked some complaints to media watchdog Ofcom.
"I would never condone anything that I thought was salacious or titillating or gratuitous," Lancashire stated.
"Yes, it was a sustained attack against a woman, but she was a police officer. Now, I don't think any of the furore would've happened if that had been two blokes.
"You have to be honest and that was an absolute, honest portrayal of what a female police officer is subjected to."
Royce may be locked up, but Lancashire does not believe Cawood has won.
"Catherine's the mother of a dead girl. She'll never be a winner. It'll never be over for Catherine. She's a survivor, but there are no winners."
Viewers will have to steel themselves for what lies ahead over the next six weeks.
"By the end of the piece, you just know that the next 10 years are going to be hell," Lancashire said.
:: Happy Valley is broadcast on BBC One on February 9 at 9pm.