It's a real-life horror story: Wellington Library's most-overdue book has been revealed, and its borrower owes a theoretical $6852 in fines.

The Dunwich Horror and Others, by HP Lovecraft, was due back on February 12, 1988.

Although the library charges fines at 80c a day, it sets a cutoff at 28 days, meaning the borrower, if he or she is eventually tracked down, will be liable for a fine of only $22.40.

The Dunwich Horror, first published in 1963, is a collection of horror, sci-fi and fantasy short stories.

Lovecraft was a huge influence on former Hobbit director Guillermo del Toro, who has been rumoured to be wanting to turn one of Lovecraft's other books, At The Mountains Of Madness, into a film.

Wellington libraries manager Jane Hill said the 28-day fine limit was there to give people a reason to return books without charging them out of house and home.

"We don't want to charge the Earth. What we're trying to do is to get the books back."

She said the library had gone through all processes to get hold of both the book and fines.

"They would have received three letters and three contacts. After that it goes to the debt collection agency, then it can go to court.

"We tend to follow up quite quickly [and] most people are upfront and pay.

"This is the only book from this long ago. Nothing else comes close to this."