A little older and wiser after receiving only an honorable mention in the school science fair, inveterate list-maker Phineas “Mac” Maguire revises his fourth-grade goals from “1. To be the best fourth-grade scientist ever. 2. To be the best fourth-grade scientist ever. 3. To be the best fourth-grade scientist ever,” to a rather less ambitious set. This revision itself undergoes more changes as Mac struggles to convince the population of Woodbrook Elementary School of the wonders of slime molds, to negotiate a bearable relationship with his Teenage Girl Space Alien babysitter and to manage the class-president campaign of his best friend Ben, who everyone, Ben included, agrees is not presidential material. Mac’s chatty first-person narration is punctuated by list after list, his character marked by both a disarming awareness of his own flaws and an unshakable faith in his friends’ strengths. His manufacture of penicillin for a friend’s Girl Scout badge is both informative and done entirely without ego, just one example of what makes Mac one of the most charmingly engaging new characters in the modern chapter-book scene. The mold experiments appended are an added bonus. (Fiction. 8-12)