Arthur Popper helps out in his family's Boulder, Colorado, junk store, Universal Trash, a place so full of cool stuff it inspires awe in first-time shoppers. When it comes to ukuleles, peppermills, and rhinestones, Arthur knows what's what. But unlike his motorcycle-riding grandma and his namesake, King Arthur, he's not brave or adventurous.

Then Arthur finds a chipped teacup, of all things, and realizes it's the key to solving the perfect crime--a crime only he knows about.

With help from a supernatural sidekick, his best friend, his annoying little sister, and a sad-faced police officer, Arthur embarks on the hard work of detecting. Everyone knows Arthur is good at customer service. Does he have what it takes to solve a mystery and confront a thief?