When mysterious things start happening at Camp Crump, they call in the intrepid detective Investigator. Each page has several questions about the illustration.

Investigator accompanies his niece Gabby to Parents' Day at school, where he demonstrates his powers of observation and helps to solve some minor mysteries. The reader is asked to answer questions about each illustration.

When his nephew disappears while trick-or-treating, Investigator faces some creepy creatures at the mysterious house of Dr. Quacker. The reader is asked to answer questions about each illustration.