This is solid middle-grade mystery done right. Lisa Yee and Dan Santat are heavy hitters in kids' lit, and it shows—the premise is fun without being gimmicky, the characters celebrate being different, and the mystery has enough layers to keep kids turning pages.

The 'awkward underdogs saving the day' angle is catnip for kids who don't see themselves as the popular crowd, and let's be honest, that's most kids at some point. The covert spy agency angle adds just enough cool factor without veering into trying-too-hard territory.

It's a series, so if your kid likes Book 1, you've got built-in reading momentum. And with a 4.7 Amazon rating and NYT Bestseller status, this isn't just parent-approved—kids are actually reading and enjoying it. That's the sweet spot.