In her 20th-floor apartment on the East Side of Manhattan, on a recent Saturday afternoon, Barbara Roston was busy explaining that she was definitely not a thief.

“It was a youthful indiscretion,” she said, “I didn’t mean to steal it.”

And yet, there it was, sitting on her desk: A faded green copy of “Gone With the Wind,” by Margaret Mitchell, that belonged to the Brooklyn Public Library.

It was 57 years overdue.

In her retirement, Ms. Roston, 72, decided to reread the book, which she had kept on her bookshelf for years, when she noticed the library’s markings.

On the last page, stuck to the paper pocket, was a sticker explaining the library’s policy: “Give your NEIGHBOR a chance to borrow this book. Return it on or before DUE DATE SHOWN ABOVE. The fee is 5¢ per calendar day for each book kept overdue.”