“I was walking to the porta potty,” she said. “I heard voices. I looked toward the barn. The light above the barn — I saw a man hit Dr. Hagerty with something. Something black that he held in his hand. Dr. Hagerty fell and I screamed. The man saw me. He pointed at me and I screamed again.” — from “Them Bones” (Minotaur Books, $29)

Who knew old bones could be worth a fortune? Rushmore McKenzie learns about dinosaurs, their bones and the black market for animal skeletons millions of years old in his 22nd thriller.

“Them Bones” refers to the skull of an armored dinosaur dug up in southeastern Montana by doctoral candidate Angela Bjork and a research team from the University of Minnesota and Macalester College. The story begins when Angela, who had recently saved McKenzie’s life, asks him to find the dino skull stolen along with the truck that was to take it to the Twin Cities.

McKenzie, a former St. Paul police officer who became a millionaire after solving a case, learns that the skull can be worth at least $6 million, but Angela and her colleagues are more concerned that the bones will be bought by a private collector who would stash it away, stopping valuable scientific research.

Since the dig is in the dusty, hot middle of nowhere, McKenzie is sure the theft was an inside job. But everyone at the site seems committed to the work and devastated about the skull’s loss. Investigations lead McKenzie to professors at both schools, students who helped dig up the bones, a high-profile black market fence, and the old man on whose land the bones were found. The skeleton will be named after him and he is willing to pay to get it back before he dies. And then there’s the intriguing, beautiful con artist Heavenly Petryk, who has crossed paths with McKenzie in previous books. She’s willing to use her chameleon personas to be a liaison between the thieves and the land owner. This gives McKenzie a chance to pretend to be Heavenly’s bodyguard, allowing him to see the inner workings of the bad guys’ scheme.

“Them Bones” is so interesting because it begins with several pages set at the dig with descriptions of how dino bones are carefully removed from the earth and wrapped to ensure no damage while transported. We see more in this book of McKenzie’s wife, Nina Truhler, owner of a St. Paul jazz club, who’s with him during a car chase. Although the story certainly has thriller moments, and we are privy to McKenzie’s thoughts via his trademark inner dialogues, this book has a lighter feel than some of the more intense offerings in this popular series. A perfect book for the light of spring.

David Housewright, winner of three Minnesota Book Awards and past president of Private Eye Writers of America, discusses his work, including his previous McKenzie book “Man in the Water,” in MELSA’s free Club Book series. 6:30 p.m. Monday, Roseville public library, 2180 N. Hamline Ave., Roseville.