"Todd's ears are so clogged up he can't hear, but he doesn't want to miss school. His teacher, the ex-spy Mr. Merlin, is sure to have secret codes for the class to figure out and a new mystery for them to solve..."
When her dog Rover is accused of tearing up Mrs. Ruston's tomato plants, Noelle investigates with her friend Todd and finds long yellow hairs that may point to the real culprit.
Todd and Noelle are volunteering at a blood drive when they get shocking news: Both banks in town have been robbed! This may be the Third-grade detectives' most important case yet.
The Third-Grade Detectives are looking forward to their field trip to a local art museum, where a priceless fifteenth-century statue of Joan of Arc is on loan from a Paris museum. But they discover the statue has been stolen. The police find the statue smashed and thrown in a Dumpster. It looks like a case for the Third Grade Detectives even if the museum director doesn't want their help.