Lexicon Adventure series

Thirteen-year-old cousins Ivan and Daphne, having lost their younger cousin, Lila, in their secret world of Lexicon, find themselves in the Land of Winter, where Lila's singing ability has landed her in a favorable social class, but they have become a slave and a servant, and they become involved in a fight to restore spring to the frozen landscape.

Thirteen-year-old cousins Ivan and Daphne are sent out to the barn on a rainy afternoon after their Great Aunt Adelaide presents them with a puzzle to solve, but a greater challenge presents itself when the cousins enter Lexicon, a world rampant with words and numbers, and embark on a quest to rescue some missing children.