The 100-Year Old Secret by Tracy Barrett follows the adventures of Xena and Xander who are related to Sherlock Holmes. They inherit his unsolved casebook from the Society for the Preservation of Famous Detectives, which Xena and Xander get invited to join because of Sherlock Holmes. The two kids take a lot of pride in solving the cases, and put all of their energy towards the cases . They work on solving a case regarding a famous painting that disappeared more than 100 years ago. They investigate together, and eventually the two children solve the case that no one else could. They are honored and everyone is amazed. This book teaches children that if you try hard enough, anything is possible. It also encourages everyone to not get discouraged and to never give up.