Bookshops are opening their doors early on Thursday morning as readers line up to get their hands on JK Rowling's first novel for adults.
The Casual Vacancy, her first full-length book in five years, is expected to fly off the shelves.
Details are few and far between and its publishers have gone to extreme lengths to keep it under wraps, with hardly any reviews appearing before its release.
But it has been described as a "blackly comic" tale about an idyllic town ripped apart by an election. It is set in Pagford, a dreamy spot with a cobbled market square and ancient abbey, which becomes a town at war with itself.
Published simultaneously in e-book and audio formats, it begins with the unexpected death of Barry Fairweather whose demise in his early-40s leaves a space on the parish council.
Booksellers took delivery of the book yesterday and the sealed boxes will only be opened minutes before shops open at 8am.
Emma Watson, who played Hermione Granger in the Harry Potter films, said she hopes readers will be open-minded about Rowling's change of direction.
"There's no way that it isn't nerve-wracking when you have so much attention on what you do and your choices and everything, but she's so wonderful and so clever and there's no way it's not going to be brilliant. I just hope that people are open-minded enough to be supportive," she said.
Rowling, 47, has amassed a fortune estimated to be around £620 million from her seven Harry Potter books for children and all the spin-off rights. She said she left "the door ajar" for a return to the world of Harry Potter but there would be no more books about the young wizard.
"There's only one reason to write now: for me," the writer told the BBC.
It was "murder" saying goodbye to her most famous character, she said.
"But truly, where Harry's story is concerned, I'm done. I just think it would be for the sake of milking it and that's just not in me.
"Now having said all of that, I have always left the door ajar because I'm not that cruel. If I had a fabulous idea that came out of that world, because I loved writing it, I would do it. But I've got to have a great idea. I don't want to go mechanically into that world and pick up odds and ends and glue them together and say 'here we go, we can sell this'.
It would make a mockery of what those books were to me. They really kept me going through some very rough times ... so I just don't want to betray them in that sense."
Rowling said she was tempted to rewrite some of the books, as "a director's cut", because she wrote them too quickly and that the next book she writes would be for slightly younger children than her Harry Potter audience.