In Poeville, weird things happen all the time.

C. Auguste Dupin enjoys snacks, cleaning his fur, and sleeping in the Reed Moore Library where his human, Penny Copper, is the librarian. When Penny's Auntie Dido asks her niece for a favor, Dupin never expected it would turn into a case requiring his considerable deductive skills.

After Penny, Dido is Dupin's favorite human. She makes the most fantastic savory sardine crackers. At first, the favor sounds simple: return a diamond necklace to Dido's amorous florist Roderick Allan. It also sounds like the perfect opportunity for more crackers. When Roderick Allan is discovered walled up in his basement, it becomes more than a case of missed naps and forgotten snacks.

Dupin wants his routine back, more crackers, Auntie Dido's dog Patches out of his hair, and Dido herself safe back at home. Which means helping Penny figure out how a simple task has gone deadly wrong!