As Menace in the Walls begins, Joshua working in a research laboratory in Cleveland General Hospital during the summer break, stumbles on a menace that has claimed the life of his beloved horse, Mandy. He is determined to solve the mystery. During the course of the book, Joshua uncovers his sister Kelley’s inadvertent link to a sinister plot involving the mysterious deaths of infants. Readers are faced with the question of whether Joshua can solve the case without putting his life and Kelley’s in danger.