My opinion : 

Natural Causes is an immersive, fast-paced crime thriller that pulls you right into a high-stakes, multi-agency investigation. Written by Nikki Stern, who takes the time to ground the story in strong character development and a vivid sense of place, this book balances swift, action-packed plot progression with deep investigative detail.

We follow P.I. Sam Tate as she attempts to settle into a quieter life in Denver after twenty years in law enforcement. Looking forward to lower-key cases alongside her trusted firm, her plans are shattered when a routine missing-person case turns into a homicide, followed almost immediately by the murder of a prominent businessman’s son. With both victims bearing cryptic one-word notes, pinpricks at the base of their necks, and ties to dark web conspiracy theories, Sam is dragged right back into the high-stress world of hunting a serial killer.

There is so much to love about this book. Stern does a fantastic job centering the plot around eco-terrorism and themes of “Mother Earth,” creating a unique narrative where every solved mystery only uncovers further secrets. The web of characters, spanning law enforcement agencies, academic experts, and an ever-growing list of suspects, makes for a fascinating puzzle. I also appreciated how the book seamlessly weaves in key points from Sam’s past. While the firm’s dynamic clearly has a strong foundation built over the previous books, Natural Causes works brilliantly as a standalone; new readers can jump right in without feeling like they missed a step.

Unlike traditional mysteries that introduce the culprit early on, Stern takes a refreshingly different approach that keeps you guessing. I kept thinking I had nailed the killer’s identity, only to realize I wasn’t even close! The story really catches fire at the halfway mark: the action intensifies, the tension amps up, and the final quarter is an absolute blast packed with shockers, high stakes, and constant twists.

I ended up flying through the entire book in one sitting. Natural Causes is a brilliantly crafted, energetic mystery that delivers memorable characters, sharp procedural authenticity, and genuine suspense. Whether you are a long-time fan of the series or looking for a thrilling new investigative read, this one is an absolute win.