The Impossible Clue — Sarah Rubin

Math whiz Alice Jones has already cracked a mystery or two. She's smart and she's fearless, so who else would her classmates turn to? But when a famous local scientist vanishes from a locked room, Alice and her detective skills graduate to the big leagues.

Dr. Learner had been working on a top-secret invisibility suit that everyone wants. Rumor has it he's disappeared under suspicious circumstances ... literally. But is wacky science really behind his vanishing? Or is it something more sinister? Alice won't stop until she knows the truth...

THE IMPOSSIBLE CLUE is a middle-grade story whose appeal is no mystery, with a protagonist whose charm needs no magnifying glass to detect.