A writer never knows where a story will be found, nor where it will lead.
For Winchester resident Kate Clifford Larson, it was in an obituary.
A historian specializing in 19th- and 20th-century women’s and African-American history, Larson found the idea for “Rosemary: The Hidden Kennedy Daughter” while reading a tribute to Kennedy on the Globe’s obituary page in 2005.
“Something about it hit me,” Larson said. “I was aware of her, but felt badly for her.”
Countless books have been written about the Kennedy family, but less was known about Rosemary until Larson’s biography. When it debuted in 2015, Larson was shocked by the public’s response. The book stayed on the New York Times bestseller list for 10 weeks, was a cover story for People magazine, and was voted one of People’s Top 10 books for 2015.
Last fall, Larson won the 16th annual Massachusetts Book Award for nonfiction.
“I’m a historian,” she said. “How often do historians get on the bestseller list? Never. I just felt happy for Rosemary and getting her story to the people in a way that they got it.”
Born Rose Marie, she was the third of nine children and eldest daughter of Joe and Rose Kennedy. Exceptionally beautiful, Rosemary was born with intellectual limitations, but still participated in family functions and social gatherings into her early 20s.
At the direction of her father, Rosemary was given a lobotomy when she was 23 that left her severely disabled, both physically and mentally. She was institutionalized, first in upstate New York and then at St. Coletta’s in Wisconsin, where she remained until her death at age 86.
Intrigued by the obituary, Larson considered exploring the story further, but decided against it, preoccupied with another project. Meanwhile, Larson’s agent had read the same obituary and called to say “I think I have your next book project.” Larson resisted, and put the idea on hold for three years.
“I figured someone else would do it,” she said.
No one did.
“Then a synergist of events happened,” Larson recalled. “My book, ‘The Assassin’s Accomplice: Mary Surratt and the Plot to Kill Abraham Lincoln’ came out [in 2008] and the Kennedy library announced that they were opening Rose Kennedy’s papers . . . her diaries, journals, photographs, and things like that.”
Larson went and pored over the Kennedy matriarch’s materials.
“Rosemary’s story emerged pretty quickly,” she said, “about how the family struggled to help her, the denials that the parents went through, and all the different schools Rosemary attended.
“It started taking on a life of its own for me,” Larson continued. “Rosemary could hold her own in the story, in the family. I knew there was an arc to the story there in the records, with [Rose] talking about the children, and [in] Rosemary’s own letters.”
What the author — from a “big, old Democratic Irish Catholic family” like the Kennedys — didn’t know is that she would find more material, publishing support, and loyal book fans in her adopted hometown of Winchester, where she and her husband, Spencer, raised their two children, Rebecca and Trevor.
Rare material — a private collection of Rosemary’s letters — came from Winchester resident Terry Marotta, an author, speaker, and syndicated columnist.
Marotta’s mother and aunt had run a small camp for girls in western Massachusetts and during the summer of 1940, Rose sent Rosemary there. The camp experience proved traumatic for everyone involved.
“Terry’s mother and aunt had no idea about the extent of Rosemary’s disabilities and the amount of care and attention the then-22-year-old girl needed,” said Larson.
Marotta shared her mother’s memories with Larson, along with correspondence between her mother with both Rosemary and Rose.
Doe Coover of the Doe Coover Agency, a Winchester neighbor who lives close by and also is Larson’s book agent, sold “Rosemary” to Boston-based publisher Houghton Mifflin Harcourt in 2015.
Years earlier, when Larson was working on her doctoral dissertation while commuting from Winchester to the University New Hampshire, Coover sold the resulting book, “Bound for the Promised Land: Harriet Tubman, Portrait of an American Hero” (2003) to Random House.
Larson spent six years working on “Rosemary.” She went back and forth in her feelings about Rose Kennedy, disliking the complex woman intensely, then feeling bad for her.
“Rose didn’t visit Rosemary for 20 years. That shocked me,” said Larson. “Although Joe Sr. struggled with the imperfection of Rosemary, there was no question that he loved his children.” He never saw Rosemary again after she was sent to Wisconsin in 1949 (He died in 1969).
“I was really hard in my view of the parents early on until my son, Trevor, was diagnosed with schizophrenia during the project,” Larson said. “That threw us in complete turmoil, not knowing what to do, trying to seek out every opportunity, every resource, to help him, and making mistakes.
“I grew an appreciation for the types of struggles Joe and Rose went through. In the end, I felt that, with the amount of money they had and the resources available to them, they misused them. On one hand, the family tried their best and on the other, they failed because they had a certain image to maintain and Rosemary suffered because of it.”
Just how hidden she was from public view became clear during interviews Larson conducted in 2008 and 2009 with two sons of Rosemary’s sister, Eunice Kennedy Shriver, who founded the Special Olympics in 1968. Timothy is now chairman of the Special Olympics, and Anthony founded Best Buddies International, which supports people with intellectual and developmental disabilities.
Both Shrivers told Larson that while they recognized how profoundly their mother was influenced by Rosemary, they had no idea what happened to their aunt.
Then Timothy came out with his own book about Rosemary, “Fully Alive,” in 2014.
“In it, he has a lot about Rosemary that wasn’t known,” Larson said. “That’s when Eunice said she had no idea for 10 years where Rosemary was and Ted [Kennedy] said he didn’t know what happened.”
Thanks to Larson’s book, Rosemary is no longer hidden. Her story has been told.
Hear Larson speak
Last year, both Winchester and Woburn selected “Rosemary: The Hidden Kennedy Daughter” as their libraries’ community reads, programs that encourage residents to come together through the reading and discussion of a common book.
Kate Clifford Larson will talk about “Rosemary:”
► Feb. 22, 7 p.m.: Shute Memorial Library, Everett
► April 28-29: Newburyport Literary Festival (time to be announced)
► May 4 6 p.m.: Lynnfield Public Library
► June 1, 6 p.m.: Peabody Institute Library, Peabody
■Correction: Because of an editing error, this story originally provided incorrect information about a talk Larson is giving about her book, “Rosemary: The Hidden Kennedy Daughter.” Clifford will appear on March 27 at the Osher Lifelong Learning Institute at Tufts. The event is not open to the public. The Globe regrets the error.