Caleb Cleveland, Kid Cop

Caleb Cleveland, Kid Cop is a series of juvenile mystery novels that exist in-universe.

History
Angus McDonald frequently reads them and gifts them, describing them as having been very formative for him.

Luca, a priest of Istus in Refuge, is also seen enjoying one of them.

Trivia

 * Likely inspired by real-life child detective series such as Encyclopedia Brown (which Taako at one point references by calling Angus by that moniker) and Nancy Drew.
 * It is an allusion to a three-part literary masterpiece written by an elementary school-aged Griffin, called "Grant Andrews: Kid Cop." Griffin and his brothers have mentioned Grant Andrews several times on their flagship podcast, "My Brother, My Brother and Me." (You can now find this book online at https://griffinriffs.wordpress.com)