DEADFALL. By Linda Fairstein, published by Dutton, an imprint of Penguin Random House, New York, N.Y. July 2017. 400 pages. $28 hardcover.

Trafficking in heroin and endangered wildlife, a stash of illegal ivory, the Bronx Zoo Skyfari and a dead district attorney for New York city. What has best-selling author Linda Fairstein gotten her lead character into now? You can find out in Deadfall — published this week and the 19th in Ms. Fairstein’s long-running series of crime novels about NYC assistant district attorney Alexandra (Coop) Cooper.

Any reader will understand why Alex wants to head for her Martha’s Vineyard home. In the past two months — which for readers means the books since 2013 — Coop has been chased by a killer on the rooftop of Grand Central Station, held hostage by gang members at Liberty Island and the Little Red Lighthouse, and tracked a murderer at the Temple of Dendur during a Fashion Week show. She has also spent two months enjoying a long-anticipated romance with her friend and partner-in-crime solving, NYPD detective Mike Chapman. No wonder she wants the quiet of Chilmark, lobsters from Larsen’s and fried clams from The Bite.

Deadfall picks up hours after the cliffhanger ending of last year’s book, Killer Look. Alex was left on the steps of the Metropolitan Museum of Art, holding the body of her slain boss, NYC district attorney Paul Battaglia. Alex is both a suspect accused of setting up the murder of her longtime mentor, with whom she had recently tangled on some ethical issues, as well as serving as a witness. While tabloids publish dramatic photos of Alex lying on the steep steps of the Met, trapped in a death grip underneath her boss’s body and with the gunshot wounds to his head visible, a task force terms the investigation into Battaglia’s death as Operation Deadfall. But was Alex Cooper the prey, the bait or the hunter?

Though technically on leave from her job, Alex pursues her own investigation of Battaglia’s death. She undertakes the endeavor with her longtime pals Chapman and Det. Mercer Wallace. Mercer, Mike and Alex know that Battaglia was silenced for a reason and they take on the task of finding out why, feeling that they owe it to their slain DA to solve his murder. Theories abound, ranging from Battaglia’s support for RICO laws targeting criminal groups to his dislike of underlings with political ambitions to his open frustration with working within the confines of his Manhattan territory, which led to his own overreach as he tried to get involved with cases with a larger purview.

Alex, Mike and Mercer begin with Battaglia’s three mysterious voicemails on Alex’s cell phone, once of which demands that she tell him what she has learned about Diana. The search leads them not to the boss’s unknown romantic entanglement but to a world unfamiliar to them all: trafficking in wild animals. The three are plunged into the world of big game hunting where millionaires pursue endangered species on private hunting reserves and conduct the paradoxical practice of preserving endangered wildlife while hunting them for trophy. A whirlwind trip to Montana gives Coop a view of Big Sky country and its Rocky Mountain bighorns as well as the leads she needs to finish solving the mystery.

Ms. Fairstein’s mastery of the crime novel form is evident in Deadfall. At just over 400 pages, Deadfall’s multiple plot and character lines are so well entangled that by the end, readers will appreciate that none of the details have been extraneous. Enjoyment of Deadfall includes not just solving the mystery of Paul Battaglia’s death but also in noting Ms. Fairstein’s craft in bringing together seemingly disparate subjects and people. A Hong Kong businessman who appeared as a minor character in Killer Look unexpectedly takes center stage, creating a bridge between the books and providing a pretext for exploring how illegal trafficking is the same around the world regardless of what the product is. The global fashion industry that Ms. Fairstein explored in the previous book also plays a role in the current one through the character of an intriguing UK-based Indian clothing designer who gives Alex her on-site experience of a Montana game reserve.

And yet the author is always careful and conscious about ensuring that a newcomer to the Alex Cooper series could pick up the latest book and be provided with enough back story to understand the context of the current action.

The author’s careful research into a major New York city landmark, which in this book is the 250 acres of the Bronx Zoo, divulges fascinating details about a place enjoyed by so many and likely taken for granted. Especially revelatory is the information Ms. Fairstein provides about the conservation and preservation efforts of the Wildlife Conservation Society, which runs the zoological park.

The 2018 entry in Ms. Fairstein’s Alex Cooper series will be the 20th in the series. At both the beginning and end of Deadfall, the author raises the possibility of a new job for Coop, one that would put her in the footsteps of the slain boss she so admired. Will Ms. Fairstein take her heroine to the next level of leading the fight against crime in New York City? Once again, readers are left with a cliff-hanging ending to ponder and the eager anticipation of Alex’s next great endeavor.

Linda Fairstein will appear at Edgartown Books on August 8 at 3 p.m. and at the Bunch of Grapes on August 20 at 4 p.m.