A series of bizarre murders that were never really solved and the beloved American novelist who never quite figured out how to write about them — it doesn't sound like the formula for a compelling book.

But in the more than capable hands of journalist Casey Cep, it adds up to a most fascinating read. Furious Hours: Murder, Fraud, and the Last Trial of Harper Lee combines true crime of the Southern gothic variety, complete with elements of race and rumors of dark magic, with an insightful biography of Harper Lee, whose Pulitzer Prize-winning 1960 novel, To Kill a Mockingbird, became one of the classics of 20th century American literature and indelibly shaped the image of the South. It's also, as far as we know, the last book Lee ever completed.

Furious Hours is Cep's first book, but her articles have appeared in the New Yorker, the New York Times and elsewhere, and often Lee has been her subject. Cep extensively covered the odd circumstances around the 2015 publication of Lee's novel Go Set a Watchman (written before Mockingbird but published 55 years after it) and, in 2016, the author's death.

The first section of Furious Hours, "The Reverend," tells the story that so captured Lee's imagination that she spent a year researching the case and many more years trying to write about it. It happened in and around Alexander City, Ala., northeast of Lee's hometown of Monroeville, the inspiration for the Maycomb of To Kill a Mockingbird.

A local man named Willie Maxwell returned to the area after serving in World War II and went to work in the textile mills and pulpwood operations. He also became a preacher for Baptist churches with black congregations (churches, and most everything else, being strictly segregated in that time and place).

Maxwell married and built a reputation as a hard and reliable worker. Tall, handsome and always elegantly dressed, he was a popular preacher. Then, in 1970, Mary Lou Maxwell, his wife of 21 years, was found brutally beaten to death in her car on the side of a road near their home.

Within days, the Rev. Maxwell filed to collect a $15,000 life insurance policy he had purchased "for twenty-five cents shortly before his wife's death," Cep writes, "shortly enough, in fact, that he never had to pay the twelve dollars required to renew it."

He was also charged with murdering her, but he was found not guilty after his neighbor, Dorcas Anderson, changed her testimony about what happened the night Mary Lou died.

Within a few months, Maxwell married Dorcas. She was dead a year later, and Maxwell's brother and nephew also died under mysterious circumstances. Maxwell had life insurance policies — often multiple ones — on all of them. In two years, he collected almost $100,000, so much that insurance companies began canceling his policies and refusing to sell him new ones.

Police investigated the deaths but never came up with enough evidence to charge him. Rumors swirled around Alexander City that he was a voodoo practitioner. Improbably enough, he got married a third time, to Ophelia Burns, who had been charged with abetting Mary Lou's death but not convicted.

Then, in the summer of 1977, 16-year-old Shirley Ann Ellington, a niece of Ophelia's whom the Maxwells had adopted, was found dead at an obviously faked accident scene. At her funeral, Robert Burns, a law-abiding truck driver who was a relative of Shirley's, stood up and shot Maxwell in the head, three times.

In the next wild twist, Burns hired lawyer Tom Radney to defend him against the murder charge. The second section of the book, "The Lawyer," dives into Radney's background and Southern politics. A white liberal who had campaigned for Robert Kennedy — which made him utterly exotic in rural Alabama — Radney had for years been Maxwell's attorney, in the case of Mary Lou's death and in civil suits against the insurance companies.

Radney had profited from those insurance policies, but he cheerfully set about defending the man who killed his former client (in front of about 300 witnesses) with a highly risky insanity defense.

In "The Writer," the third section of Furious Hours, Cep analyzes the reasons for Lee's interest in the trial by looking at her entire life. Lee had cut her teeth in courtrooms; the daughter of an esteemed lawyer, A.C. Lee (the model for Atticus Finch), she dropped out of law school just weeks shy of graduating to pursue writing.

Cep recounts her struggles in New York City to write a novel and describes the steps that led to Mockingbird and its phenomenal success. As Lee was awaiting its publication, she undertook another task that would later help spark her interest in the Maxwell case: She signed on as Truman Capote's researcher for a New Yorker article that would become In Cold Blood, a classic of the true crime genre.

Lee and Capote had been childhood friends in Monroeville, and their long relationship was a fractious combination of love and competition. The epigraph of Furious Hours is something Lee said about Capote: "We are bound by a common anguish."

Cep doesn't directly address the claims that it was Lee who actually wrote In Cold Blood, but she makes clear what an enormous amount of work Lee put into the research — and what reservations she had about Capote's loose interpretation of "nonfiction." Their differences over In Cold Blood might have had as much to do with their later estrangement as Capote's reported resentment of Lee's celebrity (and Pulitzer).

Lee herself came to detest celebrity, and she floundered for years over a second book. Then, 17 years after Mockingbird was published, came the trail of Robert Burns, and Lee headed for Alexander City.

Cep describes how the Maxwell case appealed to Lee on many levels (not just Tom Radney's notion that he was a latter-day Atticus) — its roots in race and class in a small Southern town, its intimate but mysterious murders, its stark act of revenge. And it was an opportunity to write a true crime book whose accuracy and adherence to the truth she could control.

But that proved to be a complicated task. "Lee had committed herself to a book built from facts," Cep writes, "but when it came to the story of the Reverend Maxwell, those were hard to come by and harder still to verify."

For years, the book was rumored to be imminent: "Many people knew the title. One woman claimed to have seen a book jacket. Big Tom (Radney) had heard from Lee more than once that the book was on its way to the publisher or that the galleys were already back from the printer. ... Someone claimed Louise (Lee's sister) had read the whole thing at her kitchen table in Eufaula and declared it better than In Cold Blood."

Cep wraps the story of the book that never came to light into an account of the strange last days of Lee's life, with all its legal entanglements and questions about the publication of Go Set a Watchman, which she had long declared would never see print.

In her last years, Cep writes, Lee no longer talked about the book she called The Reverend. It "remained as mysterious as the man whose life inspired it."

That is the most tantalizing mystery Cep leaves us to contemplate: "Nelle Harper Lee's estate is sealed. The entirety of her literary assets, including whatever else exists of The Reverend, remains unpublished and unknown."

Contact Colette Bancroft at cbancroft@tampabay.com or (727) 893-8435. Follow @colettemb.

Furious Hours: Murder, Fraud, and the Last Trial of Harper Lee

By Casey Cep

Knopf, 314 pages, $26.95