The desk of Mary Higgins Clark looks remarkably ordered for one of the world’s most popular novelists. But the upkeep can be explained by spring cleaning and by a pause between projects as Clark promotes a new novel, and plans her next.

“It’s a total mess when I’m working, because I have research books here,” she says. “I get allergies easily and it was getting too dusty.”

The long-reigning “Queen of Suspense” works out of the top floor of this three-story converted ranch house, logging on to a Dell computer that is foreign to her in many ways, but just familiar enough for Clark to have mastered how to store a day’s material.

Now 85, she could have retired long ago, but worries more when not writing. She’s completed more than 40 books: mysteries, children’s stories, Christmas novels, a historical novel and memoir, “Kitchen Privileges.” She has co-written books with daughter Carol Higgins Clark and has so many ideas she’s thinking of bringing in collaborators. Her current book, “Daddy’s Gone a Hunting,” is a vintage Clark thriller featuring women in distress, tragic pasts and secret identities. It’s about an explosion at a family business and of the founder’s granddaughter — injured in the blast and a suspect.

She is a well-spoken woman with a good-natured, staccato laugh and a confident, but informal manner. She looks born to live well, to have a tennis court and swimming pool and an assistant who brings tea. But commercial fortune did not come until middle age, and her affinity for women who struggle, and prevail, is clearly personal.

Mary Higgins was born in New York City in 1927, an Irish-American whose immigrant father owned a pub. But when she was 11, her father died and the family lost their home. A brother died of meningitis when she was a teen. While in high school, she worked as a switchboard operator to help her family.

As an adult, Clark relived her mother’s tragedy. She married Warren Clark, a regional manager of Capital Airways, in 1949 and had five children. But in 1964, Warren Clark died of a heart attack; his wife became a widow and single mother, with a mortgage and small inheritance.

Clark is still amazed by the energy she had. On weekday mornings, she would give her kids breakfast and share a ride into Manhattan for her job as a radio script writer. She would dress for work in the back of the car, her friends joking that it was indecent to look at the back seat until they had reached the George Washington Bridge.

Clark always was a storyteller, and in her 20s and 30s, she wrote fiction for Collier’s, The Saturday Evening Post and other magazines.

After her husband’s death, she managed enough spare time to work on a novel about George and Martha Washington. She spent three years researching “Aspire to the Heavens,” was proud of the story, proud of the scholarship, but hated the title and wasn’t crazy about the sales. (It was reissued in 2002, far more profitably, as “Mount Vernon Love Story.”)

Her life changed with her second book, “Where Are the Children?” published in 1975. Anxious to better support herself and her children, she looked to a place she advises other writers to consult — her bookshelf.

She found volumes by Agatha Christie and Ngaio Marsh, Josephine Tey and Daphne du Maurier. She would follow a formula that has worked so well in many genres — write the kind of books you like to read.

A murder trial in New York involving a young mother accused of killing her kids gave her an idea for a story of a young mother convicted of killing her own children. She set it in Cape Cod, Mass., where Clark still spends time. When she finished, she dressed in a black and white suit and dropped off the manuscript with her agent. One of the industry’s sharpest executives, Phyllis Grann, then an editor at Simon & Schuster and later the publisher of Penguin Putnam, snapped up the book for $3,000.

“I was allowed to buy anything for $3,000 or under without going through contortions,” says Grann, who was impressed by Clark’s ability to “tell a good story” and by Clark herself.

“She is strong, she is a survivor, but always with a smile. She had recently been widowed and she had five children. I had had my first child and I kept asking, ‘How do you deal with this? How do you do that?’ ... I wanted to know how my kids could turn out as well as hers did.”

Clark has since become one of the industry’s most dependable and loyal writers, regularly turning out best-sellers for Simon & Schuster. Her U.S. sales alone top 100 million copies and, her publisher says, she continues to sell some 3 million books a year worldwide.

The greatest compliment I can receive is, ‘I read your darned book ‘til 4 in the morning, and now I’m tired.’ I say, ‘Then you got your money’s worth.’ ”