The Balkan Escape (Cassiopeia Vitt, #1)

Steve Berry's first ever eBook original finds an adventurer in a strange and forbidding land, in search of a long lost treasure, and very much in harm's way. 

As a favor to enigmatic billionaire Henrik Thorvaldsen, Cassiopeia Vitt treks into Bulgaria's Rila mountains in search of a buried stash of exceedingly rare artifacts from a bygone civilization: the ancient tomb of a Thracian king. But when her presence is discovered by a shadowy group of Russians secretly mining the area, she needs a way out. Who to trust becomes the question, and her life depends on choosing the right option.