King & Kayla and the Case of the Secret Code (King & Kayla series)

Kayla receives a mysterious letter, while Mason gets one that is almost the same. Together, the letters pose a code-breaking problem. Kayla notices an important feature: most of the words lack vowels, a discovery that helps focus the effort to interpret the message. The story follows Kayla’s attempt to understand the unusual letter, with pencil and digitally colored illustrations accompanying the case.