The King's Fifth — Scott O'Dell

Newbery Honor Book: A “stunning” historical novel of a teenager's journey from Spain to the New World in search of gold (Kirkus Reviews).

Mapmaker Esteban de Sandoval is only seventeen years old, but he has experienced much adventure, traveling to the New World to hunt for gold with the Conquistadors. Whatever treasure they find, they were expected to give one-fifth of it to the king. But Esteban is accused of withholding the king's fifth -- and of murder.
 
As he waits for his trial to begin, he recalls the experience of his journey: the men he sailed with, the young Native American girl who guided him -- and the ways that it changed him -- in this remarkable novel about Spanish colonialism by the author of such classics as Island of the Blue Dolphins.