C. J. Box's latest novel, at least until February 28, 2023 anyway. It is an entry in what he calls the "Cody Hoyt/Cassie Dewell" series, although Cody has long since been absent, and I'm pretty sure he's not coming back.
(The book series is also the basis for the TV series Big Sky, although the show deviated from the books very quickly, and—sorry—not in a good way.)
So it's Cassie, and she's settling into her life as a pretty successful private eye, based in Bozeman, Montana. A couple of cases get thrown her way: One takes her to the historic copper-smelting town of Anaconda in search of J. D. Spengler, another PI who's inexplicably vanished while trying to track down a charming con artist who's defrauded Candyce Fly of Boca Grande, Florida, of millions of dollars. (The reader knows at the end of Chapter One that Spengler has likely gone to Gumshoe Heaven.)
Cassie's second case involves an anonymous poet who penned a mysterious verse in Sir Scott's Oasis Steakhouse, Lounge, & Bar in Manhattan, Montana. (An actual place, now permanently closed, according to Google Maps.) The poem told of a hidden treasure, available to the first person finding it according to the cryptic clues contained within. Cassie's intrigued when she's called by someone claiming to be the poem's author, hiring her to see how well he's disguised his identity; if Cassie can find him, he'll give her a cool $25K.
It's not necessary, but it wouldn't hurt, to have read the previous books in the series; there are a few continuing characters who make an appearance. Also showing up unexpectedly is a character from Box's other series. No spoilers here!