While this final instalment centres around an unstable young television current affairs producer, Eloise Hay, it also features a tantalisingly fleeting appearance by one of Grimshaw's most compelling creations, former National Party Prime Minister David Hallwright, "whose sunny goofiness had concealed layers of cunning and guile", she writes.
Hallwright has moved on from being a PM and he has received a knighthood. His wife Roza, who secretly struggled with alcohol and prescription drug abuse in The Night Book and Soon, has become a huge earner by writing a series of sci-fi fantasy children's books, which have been turned into wildly popular TV programmes made in Hollywood. The Hallwrights now spend a lot of time living overseas, but Hallwright is still involved in New Zealand politics. They are glossy with wealth.
"They're just living on their millions," says Grimshaw. "He did what he wanted to do then got out and got a knighthood but he still obviously has a finger in every pie. They have become peripheral characters and in a way, it has become all about her. She has been really successful but he is still operating away."
Many readers reckon that Hallwright, with his bland mansion in Parnell, his mangled speech and his circle of acolytes, must be a close pastiche of our real-life leader, but Grimshaw has steadily denies this.
"People have always said David Hallwright was based on John Key. To me, he never was. He was a composite of different types and obviously had some features," she says.
There are other "composites" at play here too, like a crusading TV current affairs presenter called Scott Roysmith, who first appeared in Opportunity. He dresses immaculately and has a favourite word: "splendid".
Auckland has a mayor "who'd been caught having an affair with an employee". But then there's no further mention of him, dismissed as unworthy of any further interest.
Most startlingly, a key figure in the book is German internet pirate Kurt Hartmann, who lives in a crass mansion out west and, despite being a New Zealand citizen, was "spied on illegally by the GCSB at the behest of the United States". When Eloise and Roysmith go to meet Hartmann, she is struck by his appearance: 6ft 6 tall, obese, dressed in black, with a jersey "the size of a duvet" and trousers "which were necessarily stretchy, due to his height and bulk. They were poignant, unfashionable, slightly too short."
However, Grimshaw presents Kurtmann as an empathetic character. Eloise looks into his eyes and assesses him as "someone intelligent, gauche, amoral, young".
He definitely evokes someone who's been in the media a lot over the past few years but Grimshaw prefers another way of putting it: "You could say a lot of the characters are reminiscent of real people in our society. It would be more accurate to say I like the idea of writing about the types of people we are preoccupied with but I am always looking at them from different angles. Of course you are playing with real events but that's part of the entertainment of it ... Kurt Hartmann is more a comedy turn really. He is meant to be a sympathetic character, a helpful character.
"I would like to think I am sympathetic to all my characters, so even the ones who are somewhat dark, I want to write about with a degree of empathy. I never write out of dislike. I look around for what I like and even if it has comic elements of some ridiculous parts of a character, I always write out of liking for that character."
You do hope she likes Eloise Hay, with whom she plays really rough. Eloise is paranoid, living alone, drinking too much and in danger due to links to her former lover, journalist Arthur. He met a nasty end in Soon because he dug up private information concerning some really powerful people. And then, just to turn the screws, Grimshaw even makes her go to a psychiatrist. Why not? She has done it herself.
"I went to a psychiatrist to seek advice," she says. "It was a genuine inquiry. I looked him up online, I didn't even get a referral. I went into this guy and he said, 'What can I do for you?' I said, 'Well, there's a narrative to this,' and sat there for an hour and told him this story and he kept saying, 'Hang on, hang on,' because he was trying to write it all down. I found the idea of the relationship interesting, the idea that you are confiding in this person but he is not your friend. It's all business. I never went back to him but I was interested in that dynamic. I needed advice from someone who was a professional. If you're a fiction writer the situation is interesting the way you can turn it around. It's all business from my end as well."
While Eloise is a young woman who shares far too much information about her private life to people she barely knows, you could hardly say the same of her 49-year-old creator. Grimshaw doesn't like talking about herself, although she is very polite about it. Her guardedness may be, partly, she says, because she is the daughter of prominent academic, poet and novelist, C.K. Stead.
"I grew up in a family where people always wanted to know about my father, so I suppose I have a little bit of caginess about being completely frank," she says. "Although I suppose if you think about some people, who tell everybody about everything, well, I am completely the opposite. I have always had the idea that you talk about the issues, and you have a certain amount of intellectual rigour and honesty, and you keep the personal thing completely separate."
Grimshaw grew up in the house in Hobson Bay where her parents still live to this day: "they have lived there for decades and decades and decades. Parnell was a very downmarket area," she recalls. "The street was all little wee rental houses with lots of Pacific Islanders. When you went up the road on a Sunday, they would all be in their houses singing, it was wonderful. Parnell Primary was 60 per cent Pacific Island. Then, when Parnell Village was built [in the 1970s], suddenly Parnell became desirable and expensive."
It was only natural that Grimshaw, who has an older brother and a younger sister, grew up reading "all the good children's books" - Nina Bawden, Joan Aiken, the Moomintrolls - and in a household with "huge numbers" of fiction and non-fiction books, she "progressed to everything", including poetry.
"Allen Curnow lived across the road, he used to put his poems in the letterbox for Dad to read. Everybody came, Sam Hunt came driving his ambulance, with Minstrel [his famous, beloved dog]. I remember meeting James K. Baxter - he came around looking for a meal and company, I guess, and Frank Sargeson, Maurice Shadbolt."
Despite all that bookishness, Grimshaw had a small rebellion when she left school, opting to do a law degree "because I wanted to do something completely different". She also did an arts degree, then worked for two years at Simpson Grierson, where she met her husband, Paul Grimshaw, who is now a partner in Grimshaw & Co, a law firm specialising in litigation and disputes. She also worked for reputed criminal barrister Murray Gibson.
"When I knew him, at one time he had many clients charged with murder. That was an interesting time." But the law was not so interesting for her. "I enjoyed both degrees but I realised that all I wanted to do was write fiction. The thing is, I always had the sense that my father was an academic and a very good fiction writer and I seem to have been able to make my way as a fiction writer without having any hang-ups about that. I am often asked, 'Do you mind if we talk about your father?'
"I just seem to be able to just do my own thing. He and I get on very well and we do our own thing and it works fine. I can imagine if I was less confident about what I was doing, the idea of the parental presence would be heavy for me but it's not. I have always had this instinctive sense that I know exactly what I want to do and how I'm going to do it."
When Charlotte Dawson died last February, Grimshaw wrote a column for the Herald relating how they both had lived, when they were really young, for a brief time in Brooklyn Flats in central Auckland. "She was beautiful and unruly," she wrote. Brooklyn Flats "was a den of vice, disorder and talent". Grimshaw and Dawson were never flatmates but it was a time, says the writer, of partying hard, "and then I stopped".
"Children make you grow up ... kids can be the best anchor to life you can have," she wrote. "Martin Amis has a line about parenthood standing in the way of suicide, something like: well, you can't kill yourself now, because of the children. Obviously the handbrake can fail, but it's there."
Grimshaw and her husband have three children, aged 23, 20 and 15. The kids all still live at home and "their spouses probably will one day, too", she laughs.
"The quote from Martin Amis, that is one way of saving yourself, isn't it?" she says. "I regarded that as a piece of luck. Finding my way to that, for me, it was great luck. In life, there is a lot of luck involved. For women, whether you can have children, whether you want children - all those things, all the big questions. It's a wonder we're not all too terrified to do anything.
"It's always been the case that I had a much more wild youth than I would ever admit to, would be the right thing to say," she adds. "It's almost as though I had two different selves - my young self and there is this self I have made since. I have often used elements of that old self in fiction and built around them but I have not yet got to the stage where I fully, frankly write about that old self without fictionalising it.
"I can imagine a time when, you know," she says, laughing, "when the children are in their 40s, when I might actually come clean about a whole lot of stuff. I sort of think in a way, it might be quite interesting but yeah, of course, maybe never."
Much to her surprise, Grimshaw has become a dog lover. That's perfectly understandable when you meet her dog, Philip, an extremely amiable medium-sized poodle, who follows her every move and barks if there's someone at the door.
He's good for "business", too. In Starlight Peninsula, Eloise, who's cracking up, borrows her sister's dog for company. She inhales his smell, looks into his intelligent eyes and feels comforted by his "hot weight" across her legs. He makes her feel less alone.
Taking Philip for a walk twice a day, says Grimshaw, has stretched her world. People stop to admire him and, therefore, engage with her too.
She laughs. "But I can't spend two hours a day walking the dog!" Yes she can. They both get so much out of it.
Starlight Peninsula (Vintage $38) is out now.
- Canvas