Muriel Spark, the British author of darkly acerbic novels that portrayed a disquieting world drifting on diabolical undercurrents, died Thursday at a hospital in Florence. The cause of death could not be learned. She was 88.

Spark did not publish her first novel until she was almost 40, but she quickly gained admirers for her taut, comically disturbing works that often depicted odd, malevolent forces insinuating their way into the lives of ordinary people. She was best known for “The Prime of Miss Jean Brodie,” her 1961 novel about a charismatic schoolmistress.

Convert to Catholicism

After a disastrous early marriage, Spark embarked on a long period of professional uncertainty and private soul-searching before converting to Catholicism in her mid-30s. Near poverty at the time, she was rescued by a fellow Catholic convert, novelist Graham Greene, who provided her an $80 stipend every two months, accompanied by several bottles of wine – given on the condition that she never pray for him. Thus fortified, Spark wrote the first of more than 20 novels and rocketed to the heights of Britain’s literary firmament.

“It is probably no exaggeration to say that she is Britain’s pre-eminent living novelist,” writer William Boyd wrote last year.

Spark cemented her reputation with her tartly macabre third novel, “Memento Mori” (1959), in which a ghostly presence telephones elderly people with the message, “Remember you must die.” Author Evelyn Waugh praised her for a “brilliant and singularly gruesome achievement.”

Childhood inspiration

But Spark found her greatest success with “The Prime of Miss Jean Brodie,” inspired by her childhood in Edinburgh, Scotland.

In the novel, an unconventional teacher at a girls’ school in the 1930s inspires and charms her students with her love of Italy and art. But Brodie’s influence over their lives takes a darker turn, as she expresses admiration for Hitler and Mussolini and ultimately comes to dominate her students with a form of psychological control.

The novel first appeared in installments in the New Yorker and was later made into a play and a 1969 film with Maggie Smith, who won an Academy Award in the starring role.

Known for eccentricities

The success of the film allowed Spark to move to Rome and later to the Tuscan countryside. She also maintained an apartment in New York. Known for her eccentricities, she wrote in longhand in spiral notebooks ordered from Edinburgh. She refused to use pens that had been touched by anyone else.

Most of her novels were relatively short, with well-sculpted prose that revealed character through sharply edged dialogue and careful description. In her 1981 novel, “Loitering With Intent,” she dissected one unfortunate character in three sentences:

“Sir Eric was a small, timid man. He shook hands all round in a furtive way. I supposed rightly that he was the Sir Eric Findlay, K.B.E., a sugar-refining merchant whose memoirs, like the others, had not yet got farther than Chapter One: Nursery Days.”

“Muriel Spark displays a talent for the dryly comic that might be regarded as supernatural in origin, if not downright diabolic,” Washington Post critic Michael Dirda wrote in 2001, “as well as a lifelong fascination with the spooky and fantastic.”

Mixed religions

Muriel Sarah Camberg was born Feb. 1, 1918, in Edinburgh to a Jewish father and an Anglican mother. She began studying Greek and Latin at 7 and attended James Gillespie’s School for Girls, where she had a teacher named Christina Kay, who became the model for Jean Brodie.

At 19, Spark married Sydney Oswald Spark and moved to South Africa and Rhodesia, returning to Britain in 1944 after her divorce. In a 1993 interview with The Post, she described her mentally disturbed husband as “a borderline case, and I didn’t like what I found either side of the border.”

She had one son, Robin, who was raised mostly by Spark’s parents. Her son became an Orthodox Jew and grew estranged from his mother.