Is any concept as magically “forever” as childhood friendship? Whether you’re from way back in the era when they were called “chums,” or your peer group now refers to “besties,” that early bonding between kindred spirits – where each day is a new adventure to be shared and distilled – is, looking back over the decades, among a person’s most treasured experiences.

The intensity of this camaraderie in part reflects the young folks’ relative lack of Life Experiences at the time – so that each new twist and turn in the relationship can be almost overwhelming in significance and portent.

Such are the issues at play in “Sweet and Sour,” the latest middle-grade novel from Mystic author Debbi Michiko Florence, a third generation Japanese American whose previous works for teens and kids include “Keep It Together, Keiko Carter” and “Just Be Cool, Jenna Sakai.”

In the new book, Mai Hirano and Zach Koyama, 12 and 13, respectively, have been best friends since early childhood. Because their parents – also close friends – live in different parts of the county, Mai and Zach only get together during shared six-week slashes of summer at his folks’ Mystic vacation home.

Ordinarily, as Mai’s family arrives for the annual rendezvous, she would be delighted. But this year, the memory of the last time she saw Zach, when he did something that shattered her, has festered. Over their two years apart, in which Zach’s family lived in Japan, Mai has dealt with her emotions by trying to imagine the most delicious way to get back at Zach.

But, now that they’ve all gathered for the summer, Zach is as charming as always, delighted to see Mai and seems completely unaware that he did anything wrong. Is he that clueless – or did Mai somehow misinterpret what happened? The situation is complicated by the appearance of some of Zach’s school friends from across the state, making it difficult for Mai to find the right opportunity to get payback. One of these newcomers, the engaging and openly kind Celeste, innocently provides information on what Zach’s been up to since Mai saw him. But Celeste’s only-positive reports only serve to further confuse Mai. Is it possible Mai misinterpreted what happened?

“Childhood friendships are special,” Florence says in a conversation last week. “Some of them don’t last when kids grow out of them naturally; others might have up and down moments but actually endure. It’s very interesting to look back on them.”

Florence celebrates the publication of the “Sweet and Sour” with a party outside Mystic’s Bank Square Books Saturday. The novel is so Mystic-centric, Florence points out, that Bank Square Books is depicted on the front cover of the novel and Mystic Drawbridge Ice Cream is on the back.

At the party, Florence will discuss the book and teen fiction with her friend Jo Knowles, author of “Meant to Be.” There will be a scavenger hunt focused on nearby Mystic landmarks, a raffle for prizes, and treats from Nana’s Bakery and Pizza pastry chef Maddy Redden. Oh, and if you show a copy of the book at Mystic Drawbridge Ice Cream, you’ll get 50% off any size cone on the day of the event.

The nature of friendship

Florence was inspired to explore the themes of “Sweet and Sour” during the pandemic, when isolation forced her to think about how time and distance change things.

"Bob (Florence) is my husband and best friend and we enjoy being with each other, but COVID came with a lot of uncertainty,” Florence says. “I realized that I had been taking old friends for granted. Suddenly, I didn’t know if or when we’d see one another again.”

And writing about middle school kids and teens – she’s written over 20 other books and chapbooks including the Jasmine Toguchi, My Furry Foster Family and Dorothy and Toto series – it’s only natural that Florence would turn her thoughts about friendship to fiction.

“I wondered what might happen if two best friends had a misunderstanding, but it couldn’t resolve because they’re apart,” Florence says. “Mai is frustrated because she can’t see how Zach is or isn’t reacting to her hurt and anger. When you’re a kid and you’re apart and can’t resolve things, you tell stories in your head and the situation exaggerates and grows. And I wanted to explore what happens if one friend is so angry and hurt and the other is clueless that anything wrong happened.”

As the incident that sparked Mai’s anger and disappointment is two years in the past, Michiko found herself worried that too much of the narrative’s exposition would be bogged down in flashback details. Then she hit on the idea of using the book’s title as a springboard. Chapters alternate between Mai’s “sweet” and “sour” associations – past and present – of the ongoing story. Ultimately, as the book’s cover teaser suggests, Mai learns “there are three sides to every story – his, hers, and the truth.”

“For kids that age, the past is very meaningful and close,” Florence says. “And it was interesting to explore that from my perspective now. The nostalgia for childhood can be very powerful.”

“Sweet and Sour” is dedicated to Lisa Fung, with whom Florence has been friends since they were 4 in California. In fact, Fung is flying in to be at Saturday’s book party.

Home sweet Mystic

One of the major “characters” in the novel is Mystic itself. Local readers will enjoy the affectionate references to iconic images and places in the village – and the homage was intentional and even celebratory.

“This is the first time I’ve written a book or story about a place where I’m currently residing,” Florence says. “Every other book is in a made-up town because, while my parents live in Orange County, I don’t consider it home. Bob (a chemist) and I moved around because of his job before settling in Mystic. We’ve been here almost 10 years now and this is the first place that’s felt like home. We love it here and have no intention of going anywhere.”

The pandemic lockdown presented Florence with the opportunity to marinate, if you will, in the Mystic-ness of her surroundings, which added atmosphere and texture to the ongoing manuscript.

“This is very much a sheltering-in-place novel,” Florence says, “and very much a summer novel. I wrote it in the summer and, since both characters aren’t from here but just come for the summer, I was able to just enjoy the process from their perspectives as visitors to a special place. I couldn’t go anywhere, so I wrote about things I knew.”

She laughs. “When we WERE able to go out again, I realized I’d gotten the physical perspective of one scene wrong. Anyone who read it and is familiar with Mystic, would realize it couldn’t have happened the way I wrote it. So I had to figure out how to fix that.”

Florence doesn’t plot out her novels. She typically starts with a premise or a character and lets the story unfold as she writes. “A lot of the fun is just letting the characters develop and see where they take me,” she says.

Florence relies on friends and members of her writing group to read through rough drafts, but says she doesn’t have younger readers.

“A lot of the copy editors and younger assistant editors at (her publisher) Scholastic tend to be younger, so they’ll call me out. ’Nobody says that anymore,’” Florence says. She laughs. “I am working on something right now, though, and I had to ask a friend’s 12-year-old whether she and her friends still use the word ’gross.’ Turns out they do.”

If you go

Who: Debbie Michiko Florence

What: Party celebrating her new teen novel “Sweet and Sour”

When: 3 p.m. Saturday

Where: Outside Bank Square Books, 53 W. Main St., Mystic

How much: free

For more information: (860) 536-3795, www.banksquarebooks.com, www.debbimichikoflorence.com