In an afterword to 2015’s “Career of Evil,” J.K. Rowling noted that Robert Galbraith, her fictional alter ego, “has always felt like my own private playground.” On the evidence of “Troubled Blood,” the fifth and latest Galbraith novel, that playground has grown deeper and more commodious than ever. Weighing in at more than 900 pages, it is the longest, most ambitious Galbraith novel to date. It is also the focus of a controversy that seems likely to divide the book’s many potential readers.

In her new book, Rowling has created a creepy serial killer who dresses in women’s clothes to more easily reel in his female victims. That decision has generated considerable outrage in light of comments Rowling made earlier this year that angered transgender rights activists. A question quickly arises: Is the creation of such a character a legitimate aesthetic choice or is it an affront to the LGBTQ community? While I don’t pretend to know the author’s motivations, I lean toward the former interpretation. Many others will no doubt passionately disagree.

“Troubled Blood” once again features Cormoran Strike and Robin Ellacott, partners in a London-based detective agency. Like the earlier books in the series, it is independent enough to stand on its own, but is best read as part of a long, ongoing narrative whose backstory was first established in “The Cuckoo’s Calling” (2013). Strike is a former military policeman who lost a leg while serving in Afghanistan. Robin, as we eventually learn, is an emotionally scarred young woman with an affinity for the peculiar satisfactions of detective work. Together, they have solved high-profile cases but have yet to resolve their complex feelings for each other. The gradual evolution of their personal relationship is one of the central narrative threads of the series.

As “Troubled Blood” begins, it is 2014 and the Strike detective agency is flourishing. Multiple investigations are underway, and several new players have been added to the cast of characters. Things change dramatically when Strike, during a visit to his childhood home in Cornwall, agrees to look into a decades-old mystery.

Nearly 40 years before, a local doctor named Margot Bamborough left work and walked in the direction of a nearby pub, where she planned to meet a female friend for drinks. She never arrived. No body was found, and no clues ever surfaced. Strike learns the bare facts of the case from Margot’s surviving daughter, Anna, who has never stopped hoping for an answer. It is the coldest of cold cases, one that is unlikely to ever be solved. Intrigued by the sheer impossibility of the task, Strike agrees to devote one year to the case.

The investigation that follows is the centerpiece of a wide-ranging novel filled with enough characters, incidents and alternating story lines to more than justify its exorbitant length. The mystery surrounding Margot’s disappearance deepens as the novel progresses, moving through a labyrinth of lies, misdirection, faulty memories and missing witnesses. Complicating matters is the fact that the initial investigating detective suffered a breakdown, using astrology and its peculiar logic as his primary investigative tool. (Bizarrely illustrated astrological charts are scattered throughout the text.) Forced to look beyond star charts and celestial influences for answers, Strike and Robin pursue a more earthbound investigation, one that will lead, after much frustration, to a solution that is at once sad and utterly unexpected.

“Troubled Blood’s” central mystery is a strong one, and watching it unfold over the course of a protracted investigation is one of the novel’s great pleasures. But Margot’s story is just one element of a spacious narrative that has more than one story to tell. As the novel progresses, the two protagonists and their complex pasts come more into focus. Robin, whose history includes one failed marriage and the memory of sexual assault, is an admirable figure struggling to establish herself in a profession — and a world — dominated by men. Rowling also provides new insights into Cormoran Strike and the forces that have shaped him. The most significant of these are the death of his mother by drug overdose and his broken relationship with an absentee father, aging rock star Jonny Rokeby. The author pays as much attention to the quotidian details of her characters’ lives as she does to the drama at the novel’s heart.

Rowling’s greatest novelistic gifts are her ability to spin wild, intricate plots (witness the astrological elements of this latest book), and to create colorful, highly individual characters who come instantly alive on the page. Even the long-absent Margot Bamborough takes on a distinctive presence as we come to know her though the reminiscences of co-workers and friends. Controversies to the side, Rowling remains that rarest of creatures: a natural, supremely confident storyteller. For more than one reason, “Troubled Blood” will surely be among the most widely read — and widely debated — novels of the season. Let the arguments begin.

Bill Sheehan is the author of “At the Foot of the Story Tree: An Inquiry into the Fiction of Peter Straub.”

Troubled Blood

By Robert Galbraith

Mulholland. 944 pp. $29