Buying a Birkin bag is not easy. You can’t just waltz into an Hermès store and pluck one off the shelf, even if you’re prepared to drop the many thousands required to pay for it. “The great majority of people are refused a Birkin, they get told that there aren’t any available in the store, which is a lie, they just don’t want to give it to them,” explains the protagonist of Palestinian writer Yasmin Zaher’s debut novel The Coin, which this month won the Swansea University Dylan Thomas prize for authors aged 39 or under.

Zaher’s unnamed narrator, a Palestinian woman living in New York, has to get to grips with Hermès’s exclusive and elusive sales policies – which seem to privilege loyal customers – after being drawn into a Birkin reselling operation.

The Birkin scheme is just a side quest, though; her day job is teaching in a school for underprivileged boys. But the protagonist’s true occupation, in this quirky, unconventional novel, described by Elif Batuman as “bonkers” and Slavoj Žižek as a “masterpiece”, is cleaning: the meticulous, fanatical cleaning of her body and its surroundings.

She develops a routine – which she calls a “CVS Retreat”, named after the US pharmacy chain – involving scrubbing and shaving every inch of her body with products and tools bought at the chemist in a process taking three to four hours, “about the average time it takes a New York lunatic to complete the marathon”.

One spot she’s unable to clean with her Turkish hammam loofah is the square in the centre of her back. After one of her CVS Retreats, she begins to feel something “blazing and spinning” in that area, and believes it is a coin, a silver shekel, that she swallowed during a car ride as a child. Naturally, the coin becomes a fixation.

“Obsession is a very good way to create a character’s downfall,” says Zaher. The writer herself has an “inherited obsession” with cleanliness, passed down from her mother and the other women in her family. Early in the novel, the narrator says that when you enter a woman’s house, “you never think of all the madness entailed” in making it “sparkling clean”.

Working on The Coin, Zaher became more intensely fixated on hygiene, and on fashion, with which she has a “love/hate” relationship. While Zaher feels “seduced” by fashion, “it’s also a tool for discrimination, for classism, for elitism, and I despise all of those things”.

Zaher, 33, was born in Jerusalem, before leaving for Yale University at 17 to study biomedical engineering. “I come from a traditional culture. Writing wasn’t something that I thought was possible. So I went into the ‘minority path’: I studied science and I wanted to be a doctor, because that’s what people like me did. And at some point in my mid-20s, I had the courage to do what I actually wanted to do.”

She went on to study creative writing at the New School, where she was advised by the novelist Katie Kitamura. She started writing The Coin after moving to New York, drawing on Clarice Lispector’s The Passion According to GH, about a woman who undergoes an existential crisis after crushing a cockroach in her apartment. Lispector “really inspired me to write wildly, to not think too much about what I was saying, about it making sense”, or about “morality”, says Zaher.

She wrote the first draft “very quickly” – it was “so messy and so illogical and so strange” – and then spent six years editing it. Meanwhile, she worked as a journalist for the Israeli newspaper Haaretz and Agence France-Presse, covering mostly culture, and “obviously politics, because we have a lot of that”.

For most of the book, Palestine is mentioned only in glimpses; debris left in the bath after a CVS Retreat is “beautiful like summer in Palestine, uneven and seared”. The character’s “initial standpoint”, says Zaher, “is that she’s going to America and she’s going to reinvent herself as this glamorous woman who has no past, no roots, no constraints on her”, but “her past and Palestine keep bubbling up to the surface”.

The same happened to Zaher when she was writing the book: “I set out to write a novel that was fun, sexy, full of pleasures, and against my will, in a way, the past was coming up for me, and the painful present was coming up for me, and at some point I had to submit to that.” Although the character in New York is “totally fictional”, almost all of her childhood memories are Zaher’s real memories, including the swallowed coin.

By the end of the novel, we learn that during the Nakba – the forced displacement of Palestinians during the 1948 Arab-Israeli war – the protagonist’s great-grandfather’s land was seized by Israelis. The Dylan Thomas prize’s ceremony happened to fall on Nakba Day, 15 May. Publication of The Coin marked a “lifelong dream” coming true, but it has also coincided with “one of the hardest years of my life”, she says.

Being Palestinian “is a very dominant identity. You live with it all the time. You’re all the time being reminded of it, externally, internally. And even more so now,” says Zaher. “My fear is that the book gets attention because I’m Palestinian.” Yet the central character is not “this perfect victim that people expect to see in a novel written by a Palestinian writer”.

Zaher instead sees her character as “almost a perpetrator”. She is often judgmental and rude, and her relationships with students are inappropriate (one boy, Jay, regularly helps clean her classroom; she begins leaving him money, and at one point kisses him on the forehead).

“I don’t like novels where there are good people and bad people,” says Zaher. “I find that boring. I’m always attracted to novels that bring me closer to my bad, secret fantasies, my repressed bad qualities. I think it’s because reading is engaging in fantasy, and writing is also engaging in fantasy, so it’s an exploration of parts of us that we cannot live in real life.”

Aside from Lispector, key literary inspirations have been Kurt Vonnegut – “he made me understand that there’s this thing called contemporary literature” and that you “don’t have to imitate the classics” – and Michel Houellebecq. “I really connect with the loneliness of his characters, and I think he’s a very courageous writer.”

Zaher now lives in Paris, with her husband, whom she met while living in New York. She’s working on her next book, a “newsroom mystery” set in Jaffa and inspired by her time at Haaretz. Asked what impact the £20,000 prize, the UK’s most prestigious for young writers, might have on her work, she says she is generally a private person, and tries “to not think about these things”. But “it would be nice if the book would reach more people who really connect with it”.

Is she still obsessive? “After seven years of being inside this novel, I think I’m a lot less clean than I used to be, and I also care about fashion a lot less. In a way it sort of healed me of my own obsessions.”