When a leather parchment of Montezuma's map is found in great-grandfather Evans' old chest, April and the twins know this summer is going to be a memorable one. The girls want to search for it but their father is against it for some mysterious reason. With Julia's help, she and the girls convince John to go on a treasure hunt. Is Montezuma's treasure a legend or reality? Whatever the case, John insists on keeping their little treasure hunt a secret. If certain people find out about it, the family could be in danger.