Candice Carty-Williams never planned on being an author, but applied to join a writing retreat in 2016 because she felt that black British authors needed more representation in the white world of publishing. Three years down the line, sales of her debut novel Queenie are booming, a Channel 4 adaptation is in the works, and she’s just been shortlisted for the Costa book awards.

The story of a young black Londoner negotiating her love life, career and family, Queenie is, according to the judges for the Costas’ first novel category, “eminently readable, funny and thought-provoking”. It’s up for the £5,000 debut prize along with Brian Bilston’s Diary of a Somebody, about a man who decides to write a poem every day for a year; Sara Collins’s The Confessions of Frannie Langton, a historical fiction about a maid’s trial for the murder of her master and mistress; and Joanna Glen’s story of a girl who doesn’t fit in, The Other Half of Augusta Hope.

“The Candice from two years ago still wouldn’t believe it. All the stuff that’s happened has been truly mind-bending. I’m still catching up,” said Carty-Williams, who left her job as a marketing executive at Vintage, one of the UK’s biggest publishers, earlier this year.

Before the retreat, she’d never considered studying writing because she couldn’t afford to take a master’s.

“Writing came from a love of reading and a love of stories. It was not my career path, I thought I’d do my marketing job forever … in my application letter for that retreat, I wrote that I just wanted our stories to be valid and to exist. We need the representation.”

Shortlisted for book of the year at Waterstones and Foyles in addition to the Costa, Queenie was acquired for a six-figure sum in 2017 following a fierce auction and has now sold more than 23,000 copies in hardback.

“It’s been super-wild and I’m really grateful for it. Maybe I’ll be able to process this stuff in another six months, because right now I’m in shock. It’s like it’s happening to someone else,” said the author, who is currently writing her second novel about a group of friends grieving a mutual friend’s death.

“If anyone asks what I do, I just say I ‘write stuff’. I’m not yet very good at saying I wrote a novel called Queenie. I think there’s maybe a Caribbean-ness in there, I don’t be too boastful about things in case they get taken away.”

More than 700 books were put forward for this year’s awards, which recognise the most enjoyable books in five categories – novel, first novel, biography, poetry and children’s books – which then compete for the title of book of the year.

Vying for the best novel award are Jonathan Coe, chosen for Middle England, described by judges as a “funny and perceptive account of ordinary lives during an extraordinary time”; Sophie Hardach’s Confession With Blue Horses, in which two siblings delve into their childhood in East Berlin; Rowan Hisayo Buchanan’s Starling Days, deemed a “beautiful and original take on mental health” by the jury; and Joseph O’Connor’s Shadowplay, a fictionalised take on the life of Dracula author Bram Stoker.

Last year, Bart van Es’s biography The Cut Out Girl won the overall prize. This year, the biography shortlist pits Observer art critic Laura Cummings’s On Chapel Sands, an investigation into the mysterious disappearance of her mother as a child, against Jack Fairweather’s The Volunteer, about a spy who infiltrated Auschwitz. Also in contention are Lindsey Hilsum’s In Extremis, a biography of the late war correspondent Marie Colvin, and Adam Nicolson’s The Making of Poetry, a look at a year in the lives of Coleridge and the Wordsworths.

Jay Bernard’s Surge, a poetic take on the 1981 New Cross fire in south London that killed 13 young black people, is up for the poetry prize, as is fellow TS Eliot shortlistee Paul Farley. The children’s category puts titles including Malorie Blackman’s new Noughts and Crosses novel, Crossfire, and Jenny Downham’s tale of a girl trying to overcome her anger, Furious Thing, into competition.

In total, 20 books have been shortlisted for the Costas, with the winners of the individual categories to be announced on 6 January. The overall winner of the £30,000 Costa book of the year prize will be revealed on 28 January.

Costa book award shortlists 2019

First novel

Diary of a Somebody by Brian Bilston (Picador)

Queenie by Candice Carty-Williams (Trapeze)

The Confessions of Frannie Langton by Sara Collins (Viking)

The Other Half of Augusta Hope by Joanna Glen (The Borough Press)

Novel

Middle England by Jonathan Coe (Viking)

Confession With Blue Horses by Sophie Hardach (Head of Zeus)

Starling Days by Rowan Hisayo Buchanan (Sceptre)

Shadowplay by Joseph O’Connor (Harvill Secker)

Biography

On Chapel Sands by Laura Cumming (Chatto & Windus)

The Volunteer by Jack Fairweather (WH Allen)

In Extremis: The Life of War Correspondent Marie Colvin by Lindsey Hilsum (Chatto & Windus)

The Making of Poetry: Coleridge, the Wordsworths and Their Year of Marvels by Adam Nicolson (William Collins)

Poetry

Surge by Jay Bernard (Chatto & Windus)

Flèche by Mary Jean Chan (Faber & Faber)

The Mizzy by Paul Farley (Picador)

Reckless Paper Birds by John McCullough (Penned in the Margins)

Children’s books

Asha & the Spirit Bird by Jasbinder Bilan (Chicken House)

Crossfire by Malorie Blackman (Penguin)

In the Shadow of Heroes by Nicholas Bowling (Chicken House)

Furious Thing by Jenny Downham (David Fickling)