In Book 6 of The Treasure Chest

Felix and Maisie take a trip to New York City to visit their father and meet his new girlfriend. While there, Maisie reveals to Felix that she has a jeweled crown she took from The Treasure Chest.

The twins travel to Hawaii in the late 1800s, where they spend time with the royal family and continue to master the magic of time-travel. There, they meet a young girl named Lydia who will one day grow up to be Queen Liliuokalani, the last queen of Hawaii.