The clue in the crossword cipher

Nancy Drew travels to Peru to solve a mystery involving a long-lost treasure and a crossword clue carved into an ancient wooden plaque.

Grosset & Dunlap
1992
9780448095448
book
Lexile: 
770

Holdings

hidmidmiidnidwidlocation_codelocationbarcodecallnumdeweycreatedupdated
386547421032322614048270829ELBA170ELB1000112JF KEE100015774597521709567815
392189421546522624048270829GENE223GENE12094FIC KEE100015774597521709567815
1678544529332422454048270829WCES509027024278FIC MYS KEE100015825759371709307855
2256660580620512764048270829LIS287T0300007Fic Kee100016159188961615918896
2256661580620512764048270829LIS287T0300024Fic Kee100016159188961615918896
2736127622762520934048270829GMI291GMG0010022SER ND100016377825731695044385
2990138645439421374048270829PCE301PCC0008278Fic Kee100016377825731695044385
327154766776351576404827082934152T 3409189FIC KEE100016407292551640729255
3450234682748515934048270829Edison16932616000011037FIC KEE100016407292551640729255