(Reuters) - The cover of Harry Potter author J.K. Rowling's first foray into adult fiction features a large black "X" in what appears to be a box on a ballot paper set against a bright yellow and red background, her publishers revealed on Tuesday.

"The Casual Vacancy" hits shelves on September 27 and has been described in a brief synopsis by publishers Little, Brown as "a big novel about a small town".

The 512-page book will be set in a seemingly idyllic English town called Pagford and centre around an election to the parish council following the shock death of Barry Fairbrother in his early 40s.

Publishers previously promised a "blackly comic, thought-provoking and constantly surprising" story. The surname of the character of Barry was originally given as Fairweather in an earlier press release in April. In Britain, the hardback version of The Casual Vacancy will cost 20 pounds and the ebook 11.99 pounds.

Since her seven Harry Potter novels became a global publishing phenomenon, selling an estimated 450 million copies, Rowling's every move is followed closely by the industry.

The books, and a hugely successful movie franchise, helped turn her into the world's first author billionaire.

Rowling is also working on a Harry Potter encyclopedia, she announced in April, and will donate proceeds from its sale to charity. It is unlikely to appear any time soon, however, as the author warned it would be a "time-consuming job."