Move over "mommy porn." There's a new smutty read in town, but this one is for the blue-haired set. Thursdays in the Park, by Hilary Boyd, has become the geriatric demographic's answer to Fifty Shades of Grey, EL James' best-selling erotic novel about twenty-somethings Christian Grey and Anastasia Steele. Thursdays, which is being downloaded wildly on e-readers, is allegedly tapping into an audience craving "granny porn" or "gran-lit," a more mature variation of the "mommy-porn" genre defined by James. Here's a quick guide to this e-book sensation, its author, and the risks of exposing grandparents to its titillating content.

What's this book about?
Thursdays in the Park is about a grandmother named Jeanie who encounters Ray, the "man of her dreams," by a swing set while escorting her grandkids to the park. Jeanie becomes conflicted, torn between her commitment to her 30-year marriage (a sexless, unsatisfactory union) and her desire for a sexually fulfilling life with a new partner. 

Who's the author?
Boyd is a 62-year-old Brit, wife, grandmother, former marriage counselor, and first-time author. She got the idea for the novel while babysitting her granddaughter in the park, which struck her as an ideal place to find romance. Boyd said she had a hunch she was tapping into an under-served but keen readership. "Old people falling in love and having passionate relationships is not a story that's had much exposure before, but I'm in no doubt the market's out there."

And the book has really sold?
Not at first. The book sank when it was published last year, selling fewer than 1,000 copies. But its British publisher Quercus reprinted it this past August, introducing an e-book version that has taken off surprisingly, thanks mostly to word-of-mouth advertising. Thursdays has topped Amazon's bestseller charts in the U.K. for four weeks, even beating out one of the Fifty Shades books. The book has now been translated into several languages and famed British actor Charles Dance is rumored to be acquiring rights to create a film version.

But is it as dirty as Fifty Shades?
Hardly. These grandparents aren't exploring their S&M fantasies. But it is a "steamy tale of sex and sixtysomethings," says Max Davidson at The Telegraph, something one might describe as "Kama Sutra meets The Antiques Roadshow." When asked about the book's Fifty comparisons, Boyd says her novel is much more pleasurable than James': "All I can say is that sex in the park beats sex in the basement."

And we're all OK with the advent of granny porn?
To a degree, yes, continues Davidson. "It is good that older people are being presented in a positive, outgoing light, not portrayed as sexually extinct." And you might as well get used to it, says Terence Blacker in The Independent, because the retired set is a significant and growing market that is finally getting noticed by the entertainment industry. See the recent box office hits Hope Springs, starring Meryl Streep and Tommy Lee Jones as a longtime married couple finding their mojo, as well as The Best Exotic Marigold Hotel. The success of the latter, based on Deborah Moggach's novel of late love and rebellion, These Foolish Things, surprised "film critics and executives as much... as Thursdays in the Park has startled the book world." And the reviews of the book aren't half bad. Chicklit Club, for example, declares it "a poignant portrait of a stale marriage and the ties that bind couples together."

Sources: The Daily Mail, Huffington PostThe Independent, The Stir, The Telegraph