Cartographer John Graf, shunned by his Amish community for pursuing higher education, becomes embroiled in a mystery when the remains of 17th-century mapmaker Cellarius, the subject of centuries-old conjecture, emerge from a German bog. The discovery of his corpse and a ruby clutched in his death grip gives credence to the existence of the fabled Tavernier Stones, a cache of the world's most prized missing jewels. Graf joins forces with a gemologist-turned-grifter to solve a puzzle Cellarius encoded into his final and most famous map.