When a private investigator from Florida disappears while searching for a man he's tracked to the small, insular town of Anaconda, Montana, his desperate client contacts Cassie Dewell to take up the unresolved case. Candyce Fly is an angry woman on a mission who wants the head of the conman who wooed her and then absconded with her money. He'd used a lot of charm and sweet talk to get her to help fund his new business venture but never returned from the meeting with their supposed prospective business partners. A case of fraud, a quickly paid retainer, a missing fellow P.I., and Cassie agrees to take on the case. However, she soon discovers the people of Anaconda don't want another P.I. nosing around in their business. At nearly the same time, Cassie receives the request to take on another intriguing case.

A mysterious poem left written on a Montanan restaurant's "Special of the Day" whiteboard promised a fortune to whoever could figure out the riddle it contained, leading to a golden treasure. Anonymous online posts in social media followed and seemed to legitimize the claim, and treasure hunters from around the world flocked to Montana to solve the puzzle and strike it rich. The hunt for Sir Scott's Treasure had captured the world's imagination, and death had taken the lives of five careless seekers.

Cassie was inclined to believe the treasure was a cruel hoax until she received a call from a man disguising his voice who said he was the person behind the poem. He wants to pay Cassie to try and locate him, claiming that others could just guess where the treasure was hidden from his writings rather than decipher the clues hidden in the poem, defeating the whole purpose and ruining the adventure. When the high retainer she quoted the man, in hopes of putting him off, arrived at her office within hours, Cassie decided he was on the level and reluctantly accepted his challenge, determined to find the man and convince him to shut down his dangerous game.

TREASURE STATE is the fifth Cassie Dewell novel and the sixth entry in the often-dark and sinister Highway Quartet series by renowned author C.J. Box. With two intriguing cases to solve, the action and investigative work are non-stop until the answers to all our questions are revealed. This may well be one of my favorites featuring this character.

I have always enjoyed the Cassie Dewell character; she seems like a normal woman, trying to keep her family together and her life on course. In this book, she's hard at work, her fledgling private investigation firm solvent but still precarious, struggling to balance her mother-daughter and boss-employee relationship with Isabel. A new addition to the firm is summer intern April Pickett from Saddlestring, Wyoming, and a crossover character from Box's popular Joe Pickett mystery series. Cassie has some of the same concerns many others experience, such as maintaining her weight and physical fitness as middle-age gains ground.

The dual plotline easily held my interest as Cassie follows lead after lead to potential new witnesses or suspects. There are several twists and turns to shock and surprise, and I know I was completely caught off guard by them. As in some previous Box novels, the villain is known from the beginning, and the author pulls out all the stops, making him a truly awful human being. I was wholly invested in Cassie taking this guy down. Balancing his undeniably evil presence, though, is the surprise reappearance of sweet Kyle Westergaard, now a young man grown, caring for the woman who had cared for him when he needed it most as a child.

With its riveting plots and engaging characters, I recommend TREASURE STATE to traditional mystery fans, especially those who have enjoyed the previous books in the series or would enjoy a compelling story of murder and deceit set in the 'Treasure State' of Montana.