Roddy Doyle’s new novel might be the best thing he has written, and I qualify that only because it’s the third book featuring his character Paula Spencer, and the previous two remain the high points of his output. In The Woman Who Walked Into Doors (1996) and Paula Spencer (2006), the character of Paula – Dubliner, mother, cleaner, alcoholic, domestic abuse survivor – gave us masterpieces of empathy, economy and unexpected humour. You don’t need to have read them to enjoy The Women Behind the Door, though you’ll surely want to once you’ve finished it.

To bring newcomers up to speed, in the first book Paula’s brutal thug of a husband, Charlo, got what he deserved – a frying pan to the head – and was later shot dead by police. (Paula would rather have been a divorcee – “it’s a great word, as sexy as fuck” – than a widow.) In the second, she was struggling to stay off the drink – making the beds all day to keep her mind and hands busy – and raising four children.

As her new story opens, it’s May 2021 and things seem bright for Paula, who’s now 66. “She’s had a great day.” We meet her best friend, Mary: they both work at a dry cleaners and share more laughs than she ever thought possible. “Paula sometimes wished that she’d met Mary sooner in her life. But she knew – Mary wouldn’t have been her friend now. She’d have given up on Paula decades ago – 40 years ago. […] It was better this way.”

She’s in a casual relationship with Joe, an older man from posh Howth. “That was the difference – a difference – between them. Joe couldn’t eat a piece of cake without a fork – Paula didn’t even need her hands.” They’re temporarily separated by Covid restrictions, and “she doesn’t miss him. But she wants him to phone her, all the same.” Of her children, Paula remains closest to her eldest, Nicola, the one who seems to have risen above her wrong beginnings. She loves being out with Nicola. “She’s my daughter, Paula wants to shout. Believe it or not. She came out of me.”

The first chapter of The Women Behind the Door, which takes up a quarter of the book, is perfect because it captures everything. The banter between Paula and Mary, her ever-present memories of Charlo, and her feelings on being a parent of middle-aged children. Doyle’s control is so nuanced that on one page I was first laughing at Paula’s worries how to organise her children’s names on her phone without offending anyone – and then fighting back tears when she sees Nicola’s name and thinks: “That’s the number she’s phoned most often – that’s the number that’s saved her.”

Doyle pushes the reader’s buttons by opening Paula to us in her entirety: strength and vulnerability. Nothing is hidden: we get her opposing thoughts, such as how she remains traumatised by Charlo’s violence, but can still remember the time “when his tongue on her neck could make her disappear”.

Most of all, she tortures herself with complicated feelings for Nicola. “She wonders if she’ll ever catch up with it – the fact that Nicola isn’t her fairy godmother. She’ll have to. She wants to.” She will: it’s coming. As the tone of the book darkens, a hundred-page scene with just mother and daughter makes Paula wonder if Nicola really did climb clear, or whether the “badness” in her life could not be cut out.

Paula loves Nicola but also resents her because of her perfection. Yet she fears now – as her daughter prepares to tell her “something she wouldn’t survive hearing” – that she has damaged Nicola’s perfect life. And she feels guilty about that – which she then takes out on Nicola. It’s heady stuff, a brew of emotional turmoil that shows how we all contain multitudes and contradict ourselves. And all this is delivered in a scene that consists of no more than two women talking.

In one sense, The Women Behind the Door is a gloomy book: it shows how Paula, and Nicola, and all of us, can act against our own better judgment. It reminds us how, as Graham Greene put it in The Quiet American: “We all get involved in a moment of emotion and then we can’t get out.” But it’s full of energy and life, it completes a trilogy to read and reread, and it shows us finally, joyously, how, whatever life throws at Paula Spencer, “she’ll manage. She always has.”

• The Women Behind the Door by Roddy Doyle is published by Jonathan Cape (£20). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply