Camelot, his widow's vision of his presidency as a noble era, has since become a romantic fiction but our fascination with JFK and his clan hasn't waned. From museum exhibitions celebrating Jackie's wardrobe to lurid accounts of the late John Jnr's marriage, the family continues to stoke the public's imagination and now The Importance of Being Kennedy, a new novel by Laurie Graham, is a fresh perspective on the most infamous IrishAmerican family of the 20th century.

The book is written from the viewpoint of Nora Brennan, a girl from Westmeath who emigrates to Massachusetts in 1917. She lands a job as nursemaid to the Kennedy family and bears witness to every moment in the lives of Joseph and Rose Kennedy and their brood of nine children. The boys are primed to take over a dynasty, the girls are taught to be good, supportive and dismissive wives but all have been instilled with the belief that the laws governing ordinary people do not apply to the Kennedys. Joe is a warm and dominating father while Rose is a cold and unbending matriarch, and Nora Brennan is privy to all the family secrets.

"They've been on my radar for more than 40 years. They've been very much part of the mythology of the 20th century that I've grown up in, " says Graham, explaining her impetus for writing the book. "The thing that strikes you about them is that they're the finest example you could look for of hubris, which is a very tempting subject for any novelist. What made them very attractive to me is that it's very much a family story as well. It's astonishing what havoc two determined parents can wreak in the creation of a dynasty."

Graham has now written several novels based on real events and people and says that she will do some reading but doesn't spend months in libraries going back to primary sources because, "I'm not a biographer. My idea is always to tell what is actually a very well-known story but from a fresh point of view. I decided the best place to stand to tell the story was below stairs because the Kennedys are typical of people who have come up first in the world. They get staff, they soon forget that the staff have eyes, ears and brains of their own." Very few Kennedy staff members have written about them, except for one of Rose's secretaries and one of her drivers, but none of the Irish nursery maids of which there had been many over the years. Thus, Graham found the voice of Nora.

The compelling angle to Graham's book is her focus on the two Kennedy daughters who were subsequently written out of the family history: Kathleen (nicknamed Kick) and Rosemary. Kick was the fourth child and second daughter, an attractive and vivacious girl who incurred her mother's wrath when she married Billy Cavendish, the Marquess of Hartington and a Protestant. When he was killed in World War II, she became the mistress of Peter Wentworth-FitzWilliam, the 8th Earl FitzWilliam, and they planned to marry after his divorce. On their way to visit her father, they were killed in a plane crash. Only Joe Snr attended her funeral and Rose discouraged other family members from attending because Kick had married outside the church.

It would be five years before Rose visited her grave.

"Many people have said to me since they started to read the book, 'Oh, I didn't even know about Kathleen, never heard of her, '" Graham says. Rosemary is another family member who was to all intents and purposes airbrushed from the family tree. Possibly dyslexic and with learning difficulties, she was a simple uncomplicated girl who tried to keep up with her brothers and sisters but who began to suffer from violent mood swings as she got older. She also became interested in the opposite sex which horrified her parents and they arranged for her to have a frontal lobotomy at the age of 23. Instead of making her more docile, the operation left her with the mentality of a baby. She spent the rest of her life in residential institutions and died in 2005 at the age of 86. "What I think makes it all the more tragic is that you look at the Kennedy men and how sexually incontinent they all were and that one of the girls was so destroyed simply for wanting what they helped themselves to all their lives, " Graham says.

Rose, she believes, is a very interesting case study.

She grew up around politics and chose to marry Joe Kennedy and settle down into the life of a good Catholic wife and mother, but was clearly very frustrated and would have loved a political career. It was when the boys came to maturity and started to run for office that she stopped her incessant travelling and really came into her own.

"When the children were small, she was never really there. But when the boys were grown up and starting to do something that interested her, she just rolled up her sleeves and that was when she was happiest. And she expected her daughters to do the same, to support the brothers but not to have any political ambitions of their own."

Overall, it's a deeply unflattering portrait of the matriarch and Graham is conscious of this. "The thing that troubled me once the book was finished was that clearly Rose and Joe were equally culpable. They planned the family they created, yet I know that Joe, for all his terrible faults, comes across as a more sympathetic individual than Rose does. I guess one expects a woman and mother particularly to have more compassion than she ever showed. This terrific self-discipline that brought her a lot of admiration and people in America still talk about her great composure and dignity in the face of all the deaths of her children. But it also speaks of something else, of a coldness at the heart of her."

Does Graham believe in the Kennedy curse? "Not in the traditional sense but it depends on how you want to define it", she says. "I think the curse of the Kennedys was Joe and Rose. It's that simple. If you look at all of the things that have happened to them, they all amount to one thing, which is arrogance.

The idea that rules that apply whether it's the legal rules or the laws of nature, they think they can defy them. This is how they were raised to think, that the Kennedys were different from everyone else."

'The Importance of Being Kennedy' (Fourth Estate) by Laurie Graham is out now