A clue takes Amy and Dan Cahill to Egypt, where they investigate the origins of the rivalry between the Tomas and Ekaterina branches of their family and try to figure out if they can trust a message from their dead grandmother Grace.

Dan and Amy Cahill are the latest guardians of the Clues which consists of thirty-nine ingredients in a serum that transforms whomever takes it into the most powerful person on earth. They think they've done everything right, but a tiny mistake leads to catastrophe.

Amy and Dan Cahill travel to Australia to figure out what their own parents knew about the object of their quest, but their search brings back terrible memories for Amy and endangers a secret ally.

After seven members of their family are kidnapped by an organization called the Vespers, Dan and Amy Cahill must race against time to track down an ancient map to pay as ransom to bring the hostages home.