Hidden among Sid Johnson's most treasured possessions is a letter he promised to take to Santa Fe. Is the letter a family history as he's been told or the key to a long-forgotten Spanish treasure? Why is its code name Esteban's Cross? All Sid knows is that he trusts the man who gave it to him and others are willing to kill for it. But the letter is pushed to the back of his mind as he learns firsthand that travelers on the trails west have more to fear from disease than from the American Indians they are displacing. As he grieves over losing his home and friends, Sid must deal with an unwelcoming group of boys in the wagon train. And as if things couldn't be worse, he discovers the letter is missing just when he needs it to save his little sister from kidnappers. Sid learns what true friendship and courage mean as he navigates life's challenges on the Santa Fe Trail.