When Mari Baroja is found poisoned at the Durant Home for Assisted Living, Sheriff Longmire is drawn into an investigation that reaches fifty years into the mysterious woman's past. Her connections to Wyoming's Basque community, the lucrative coal-bed methane industry, and the personal life of the previous sheriff, Lucian Connally, lead to a complex web of half-truths and assumed alliances.
Aided by his friend Henry Standing Bear, Deputy Victoria Moretti and newcomer Santiago Saizarbitoria, Sheriff Longmire must connect the present with the spectre of the past to find the killer.