There are plenty of early 90s touchstones that pepper Tegan and Sara’s elegant and evocative memoir High School, which tells the story of their teenage years in Calgary, Canada. There are Kurt Cobain shrines, mosh pits at Green Day shows, teenagers playing Street Fighter in arcades. The most 90s of all, however, is how much time the twins spend on the telephone. Friendships, love affairs and messy personal sagas all take place over a shared landline.

Today, Tegan and Sara Quin are calling separately from their homes close to each other in Vancouver to explain why they have decided to revisit their adolescence in great, probing detail. To listen to them chatting away down the line is apt. It brings the book so vividly to life that I almost find myself twirling an imaginary cord around my finger.

The Quins were supposed to have a break after they finished touring their 2016 album, Love You to Death, but they quickly grew bored of the down time. At the end of that year, they set up the Tegan and Sara Foundation, a charity that campaigns and fundraises for LGBT women and girls. Then they talked about doing a live record or starting a podcast. They also wrote a book proposal.

Of all the creative projects, the book proposal stuck. “It got into a bidding war and sold, and I was like: ‘Holy fuck, we have to write a book,’” Tegan laughs. High School tells their story from 15 to 18, when they first took drugs, got girlfriends and picked up guitars. “If people really want to hear the origin story of our band, that started in high school, and that coincided with our figuring out we were queer. It felt like a very lush time to go back to and write about.”

Facebook Twitter Pinterest ‘It wasn’t until 2008 or 2009 that people started to say: ‘How have you guys existed for 10 years? How do you keep getting these huge tours?’ Tegan (right) and Sara on stage with Taylor Swift in Los Angeles in 2013. Photograph: Christopher Polk/TAS

High School ends just as Tegan and Sara the band really begins, but their subsequent career could fill a few more volumes. They released three well-received indie-rock albums in the late 90s and early 00s, but it was their fourth album, 2004’s So Jealous, that brought more attention; the following year, the White Stripes, then at the peak of their fame, covered Walking With a Ghost, one of its standout tracks.

In 2013, after two more albums and more years of steady-build success, there was another crucial shift when they went all-out pop with Heartthrob, a record stuffed with hits that landed them on the arena pop circuit. They supported Katy Perry, Paramore and Taylor Swift, who cited them as a key influence on her album 1989. They performed on Everything Is Awesome, the blockbuster theme tune for The Lego Movie.

Even so, they often had to fight to be there. When So Jealous came out, they faced snide comments from the music press about their sexuality, as well as an assumption that their music was for young girls only. “It wasn’t until we hit 2008 or 2009 that people started to actually say: ‘Holy shit, how have you guys existed for 10 years? How do you keep making records? How do you keep getting these huge tours?’” Tegan recalls. They had been out as queer women since the start of their career, but, at times, they felt alone in that, too. “We always felt like no one wanted to be lumped in with the Tegan and Sara kind of gay, and that always hurt our feelings, because we were like: ‘What’s wrong with us?’” Sara says. “Like: ‘Why aren’t we cool-gay? Why are these other artists cool-gay and we’re not cool-gay?’”

They are about to turn 39 and will this month release a ninth album, Hey, I’m Just Like You. It harnesses the same synth-pop sounds as its two immediate predecessors, but it swerves off the road, just a little. They have taken songs they came up with as teenagers, the ones the book describes them furtively practising at high school, and reworked them for Tegan and Sara today. “Who goes back and takes their first songs and says: ‘No, these are as good as anything we’ve ever done and we’re going to put them out at the peak of our career?’” says Tegan, proudly. “We like to stir things up.”

Facebook Twitter Pinterest ‘We’ve been around for 20 years and we just keep growing’ ... Tegan (right) and Sara perform in the semi-final of Garage Warz, a music competition in Calgary, in 1998. They went on to win it.

In High School, each of the Quins takes a turn at a chapter; today, as in the memoir, Tegan has a more garrulous, upbeat take on their history, shared and otherwise. For many people, adolescence was mortifying – why would anyone want to return to it? “We get asked this question a lot, but it’s important,” says Sara. She is recovering from a cold and seems more reflective, less gung-ho. “Everyone says the same thing: it’s embarrassing, my hair, my clothes, my face, my choices, yada yada yada. But then I think of some of the most significant social cultural things right now, and they’re all centred on high school, like [the television dramas] Euphoria and Sex Education, and some of [the music by the singer] Billie Eilish. There’s this duality of disgust, and then being preoccupied with it.”

This is a version of the answer she has become used to giving, but she is starting to think there may be more to it than simply showing youth the respect it deserves. “Talking to you now, I’m having a slight epiphany. It occurred to me that, as an artist, I feel very insecure. I have a lot of self-hatred: some of it is internalised homophobia, some of it is ... I don’t know what.” In High School, Sara appears the most bruised by the teenage experience. She writes about puberty as “the time my body began to betray me”; her fears for their futures as queer women in the early 90s, when gay marriage, gay adoption and even gay role models were not part of everyday life, are palpable on the page. “Writing the memoir made me realise that a significant amount of my self-hatred comes from when I was in high school. This sort of profound discomfort with my body and with my mind, and so much of that shame in feelings of lust and desire, and sexuality that becomes so distressing and all-consuming.”

She says that she still has a lot of those feelings. “I think, going back and writing the memoir and listening to that music, I had this desperate hope that somehow I would be able to fix it and I would be able to heal the parts of me that got damaged and traumatised in that part of my life.” She laughs, before likening the process of delving into one’s youth to exposure therapy. She expected to be embarrassed by her teenage self, she says, because everyone expects that. But she ended up loving her. “I’m so amazed at what that person accomplished, knowing that inside they were really, really damaged.”

Fans of the band are fully versed in the sisters’ tempestuous relationship. When interviewed together, they often bicker; they have talked in the past about physical fights. In the book, their arguments are frequent and, in the context of the time, often quietly devastating. “We have very little access to each other’s interior world,” Tegan says today, although writing High School seems to have given each a new way into the other. “I always thought it was so weird that Sara talked about [her sexuality] so differently, and then I read her side of the book and I was like: ‘Oh! We have very different experiences.’” It is one of the misconceptions about twins, she says – to assume they must have lived the same life. “We grew up in the same house. We were treated the same, and yet we had such different experiences and different struggles.”

We never talk about women and drug use positively. It’s men who write about psychedelics and science and mental health Tegan Quin

Tegan speaks and writes with practised frankness about her early lack of comfort with her sexuality. “You can’t understate the significance of how little representation there was. There were a few small, very one-dimensional looks at queer identity in the mainstream. So the movie Chasing Amy, or All Over Me, Rickie from My So-Called Life, or kd lang on the cover of Vanity Fair with Cindy Crawford – that was it.” That Tegan and Sara became mainstream queer pop stars themselves, filling an empty space, is less of a surprise after reading High School, which reveals that they have always held on to a strident sense of what is right, in addition to their insecurities.

There is less of a cultural void these days, and much talk of the next generation’s openness when it comes to gender and sexual fluidity, but reading High School makes it sound as if this was always there. “I will say that, no, I do not think our experience was the norm,” says Sara. “As I’ve gotten older, I’ve realised more and more how totally unique and almost futuristic it was. I don’t know how to explain it.” She puts forward a theory that their friends all gravitated towards the rave scene, a world that allowed them to explore intimacy. “There was such a queerness and a femininity about raves at that time. Everywhere we went in the rest of our world, men seemed dangerous to me. All the guys seemed dangerous and sexual and intense, and hated us, hated the way we dressed, hated the way we looked. And I remember going to a rave the first time and seeing guys holding each other’s hands and guys hugging each other and being affectionate.”

Perceptive readers will suspect there is a reason everyone was holding hands and being affectionate at a rave; High School doesn’t hold back on that, either. “Tegan and I were really into acid,” Sara explains, breezily. There was a lot of it around, and it was cheaper and easier to get hold of than alcohol. She says they discussed how much of their drug use to include in the memoir, and that she found herself defending it to their mother. “I didn’t want to sanitise or dumb down our experiences because we were afraid that people would say: ‘Oh, this is a bad influence,’ like: ‘Tegan and Sara are making acid seem cool.’ No, it was my experience. I’m almost 40 years old, I haven’t done acid in 20 years, but I also think that the stigmatisation of drugs is unhealthy, because we’re a society that is obsessed with alcohol.”

She says that her teenage experiences of drugs were, for the most part, positive. Her memories of alcohol were terrible. “I was totally terrified by the stories that I recalled of blackout drinking, choices that I made, people I hooked up with, experiences with men that could have gone in a completely different direction. I never had that with drugs, but I had that with alcohol.”

Facebook Twitter Pinterest ‘We like to stir things up’ ... Tegan (left) and Sara playing Coachella 2008 in Indio, California. Photograph: John Shearer/WireImage

Tegan suggests that women are rarely allowed to talk about drugs without it being turned into a cautionary tale. “We never, ever talk about women and drug use positively. It’s men who often write about psychedelics and science and mental health. Rock stars always have some sort of proximity to drug use, but the only time we ever hear about women and drug use is, like, Amy Winehouse and Courtney Love, and it’s a warning.” People in their lives were alarmed about them telling the more acid-heavy parts of the story, she admits. “But what’s the point in going back if you’re not going to be honest? It’s so hard to say, because I’m not proud of it, but I’m not not proud of it,” she says. “Just like: ‘We did that!’ We got it out of the way and then we got our shit together and then we went on to become these people.”

High School has an afterlife. They are working on developing it into a TV series. They have two graphic novels coming out in the next couple of years, about their younger experiences of school. There is the album, plus an intimate storytelling tour, which combines a performance with anecdotes, called An Evening With Tegan and Sara. Having had the experience of pop megastardom, with Heartthrob and I Love You to Death, I wonder if they still have ambitions to headline stadiums. Tegan says that era “pulled the curtain back” on what it means to be that kind of pop star. “It’s a lot of work. I have mad respect for the Katy Perrys and Harry Styleses and Billie Eilishes of the world. I don’t think people understand how hard what they’re doing is, and that they have no lives and no off-switch and no space. Especially pop artists. It’s hard, and I don’t want it,” she says, warmly.

Still, for a while, they had it anyway, but they have always been one step ahead, whether reshaping indie rock or releasing big pop hits about their girlfriends, right before queerness was turned into a marketable mainstream commodity. “I’ve been driving Sara crazy,” begins Tegan, “but I’m not going to minimise us any more. I’ve been calling us visionaries, and it’s partly in jest, but I’m also serious. We’ve been around for 20 years and we just keep growing.” Sara, on the other hand, says she never felt like a trailblazer. She is reluctant to claim that space for herself. “But if Tegan were here, she’d tell you that, yes, we are trailblazers.” I tell her that Tegan had, in fact, said they were visionaries. “I cannot believe she said visionaries! I told her to stop saying it,” she groans, in perfect disagreement.

High School is published on 24 September; Hey, I’m Just Like You is released on 27 September