When Jen, the largest, most complete Tyrannosaurus rex skeleton ever found, surfaces in Sherriff Walt Longmire's jurisdiction, it appears to be a windfall for the High Plains Dinosaur Museum - until Danny Lone Elk, the Cheyenne rancher on whose property the remains were discovered, turns up dead, floating face down in a turtle pond. With millions of dollars at stake, a number of groups step forward to claim her, including Danny's family, the tribe, and the federal government.

As Wyoming's acting deputy attorney and a cadre of FBI officers descend on the town, Walt is determined to find out who would benefit from Danny's death, enlisting old friends Lucian Connolly and Omar Rhoades - along with Dog and best friend Henry Standing Bear - to trawl the vast Lone Elk ranch, looking for answers to a 65-million-year-old cold case that's heating up fast.