Vicky Krieps as Ingrid and Emma Mackey as Sofia in “Hot Milk”

If you were a 25-year-old woman who’d put her life on hold to care for her wheelchair-bound mother, what would you do if at the end of a costly cure for which your mother mortgaged the family house, she said the pain in her legs was still so bad she was going to have them cut off?

To add an extra twist, what would you do if your mother told you that on rare occasions she could walk and, at the same time she is maintaining the cure did not work, you’d secretly observed her walking?

This is the crux of the psychological battle that 66-year-old retired librarian Rose (Fiona Shaw) and her daughter Sofia (Emma Mackey) have been waging throughout the Berlinale competition film “Hot Milk”, which had its premiere in Berlin on Friday and is based on the 2017 Deborah Levy bestseller of the same name.

“It was the psychology of the novel, the brilliance of the characters, the complexity of the emotions,” that made her want to film the novel, director Rebecca Lenkiewicz, a British playwright making her first feature film, told a Berlinale press conference.

And quite the emotional roller coaster it is. As the film opens, Rose and Sofia are settling into the beachside villa in Spain that Rose has rented so she can meet with the enigmatic consultant Gomez (Vincent Perez), whose credentials are unclear but whose fees are sky high. From the get go, Shaw, the Irish-born actress familiar to audiences from “Killing Eve” and the Harry Potter films, does every and anything she can to tear down Sofia. The bottled water Sofia bought doesn’t taste right. She tells the consultant that Sofia is a barista when in fact she suspended her PhD studies in anthropology to care for her mother. And for good measure Rose says her daughter will never be able to drive because she failed the driving test four times — on the written part.

Sofia, who has been putting up with her irascible mom for years, mostly sloughs it off but something is bubbling below the surface. That something gets a human face when Ingrid (Vicky Krieps), who ostensibly lives in Berlin but is staying in Spain to sew fancy duds for whoever can afford them, literally rides into Sofia’s life, on horseback along the beach while Sofia is relaxing after a swim. Thus begins the strand of the film that earned it a “Queer Coming of Age” tag on the Berlinale programme. And yes, there is lesbian sex, but Ingrid also has a black male flame named Matty, who ends up working as a driver for Sofia and Rose to get them to the far-away clinic. And Sofia, who soon after arrival is stung by one of the jellyfish infesting the coastline, seems to have a thing for the lifeguard who treats her for medusa poisoning. And treats her a second time when she is stung again.

While Sofia is spreading her wings, Rose is at first hopeful that the consultant, for whose fee of 25,000 euros she has mortgaged her house, is doing her good. He immediately takes her off several of her medications, does scans of her lower body and begins probing whether there might be something in her past, a suppressed memory, that could explain her condition. Rose, who talks vaguely about a sister who died when she was very young, resists the psychological probing. As does Ingrid, who cryptically tells Sofia that she once killed someone, but is reluctant to say more.

Sofia, in a riveting performance by Mackey, who made waves in the streaming series “Sex Education”, becomes the dervish who unravels all. On the spur of the moment she flies off to Greece (which, by the way, is where the filming took place) to visit the father who has barely seen her since he divorced Rose and started a second family in Athens. He tells her point blank he has no money to give her to further her studies in the U.S. What she concludes is that he has nothing to offer her in any respect and that will be the last time she sees him

When she returns to Spain she takes life more and more into her own hands. She starts driving, even though she has no licence. She gets Ingrid to confess that the person she murdered was her own young sister, pushed too high on a swing and not actually dead but mentally incapacitated. Sofia says this is a childhood accident, not murder.

And then she must deal with her mother, who is demanding part of the fee back from Gomez and wants to fly back to Britain to have her legs cut off. Sofia has had enough. With her newfound, if illegal, driving skills, she sets up a challenge for her mother in the final scene — walk or don’t walk, sink or swim.

It’s a situation that leads directly into the debate over assisted dying that has roiled many people and countries recently.

“It’s a big question and there’s a lot of talk about assisted dying in Britain at the moment,” director Lenkiewicz said. “In the case of Rose it’s life and death: do you choose life or do you choose the other? And I feel strongly that we hurtle into the world in birth. And death, if we are corpus menti, we should be given a choice.”

— By Michael Roddy