Hannah and Emily begin a difficult and dangerous seventeen hundred mile journey to Boston. Alone on the trail, the two girls are adopted by 'Dog' who becomes an invaluable companion and protector. In Omaha, they buy passage on a riverboat bound to St. Louis but a disaster separates them. Hannah discovers Emily and Dog are being taken down the Mississippi River to New Orleans and she follows after them. When she arrives there, she learns Emily has been kidnapped with the expectation their rich grandmother will pay a huge ransom. Hannah finds that, once again, she needs to rely on new friends, especially Dog, if she hopes to save her sister.