Superhero superfan by Megan McDonald

At a Moody family yard sale, Stink uncovers a box of old comics about a hero he’s never heard of: Super Gecko. What could be more fantastic than a superhero with lizard superpowers? Hello, fun! Even better, Super Gecko is making a comeback, and Stink quickly becomes his number-one fan. Stink starts receiving mysterious notes signed by Super Gecko himself. But Super Gecko isn’t real, is he? Using his own powers of deduction – thanks to all the cool stuff he’s learning at Saturday Science Club – can Stink figure out who is writing the letters?