Operation Robot Storm is the first of his new series wherein a hairy band of heroes (and their human friends) secretly save the world from a mad array of supervillains. The whole series is pure all-ages adventuresome fun. Action, comedy, cool gadgets, danger, twists, yaks sailing through the air: this is creativity that will spark any kid's imagination, and will keep Mom, Dad or whoever is reading to them amused. The series is perfect for reluctant readers or kids graduating into chapter books. Each new chapter opens with a few pages of comic book before blending into well-illustrated prose, and the educational content is present but never preachy.
Rather than summarize the plot of Operation Robot Storm, allow me to recommend viewing the promotional trailers on YouTube. They show what the book is about, and give a flavor for the style in which the story is told. My kid has watched each a couple dozen times, and he has gone and hooked his cousin and a friend on the Mythical 9th.
Any book comes with a few niggles, but when the most salient detraction that comes to mind is a typo, it's best to just skip to the seven-word summary: HIGHLY RECOMMENDED BY CRITICAL MICK AND SON.