Relics of the Madré Véna (2017)

Maggie Keller's PhD. is in jeopardy... Facing an anonymous accusation of plagiarism, a doctoral committee ready to expel her, and contradictory support from her academic advisor, Maggie plays a last-ditch wild-card that stalls their verdict on her dissertation, attracting the attention of Katherine Sapp, a mysterious government agent. Katherine and Tony, her Homeland Security partner, offer Maggie a deal: they will validate the graduate student's research on lost Viking-American colonies in exchange for helping them solve their investigation into an Ozark treasure mystery - the Madre Vena Ore Cache. But in doing so, Maggie must locate her estranged sister, Dutch, who may be involved in a related string of illegal cave intrusions and grave robberies with a rival Australian treasure hunter named Hawk. When the joint expedition finds the legendary cave, both siblings are reunited over the discovery of a mysterious Viking sword. But with no sign of the fabled treasure in sight, Katherine suddenly turns on Maggie and kidnaps her best friend, Simon, as collateral. Now Maggie must reluctantly team up with Hawk in a shaky alliance, racing through ghost towns, wild caves, lost cemeteries, and urban undergrounds to solve cryptic clues and stop the real source of the mystery from falling into the wrong hands!