It's a bona fide mystery at Dink's school. Some sneaky soul has stolen the skeleton from the nurse's office! The principal promises free aquarium tickets to the savvy students sleuths who can track down poor Mr. Bones. Soon mysterious clue are showing up all over the school. It's up to Dink, Josh, and Ruth Rose to follow the clues and put those old bones to rest.
After solving another mystery book in New York, Dink, Josh, and Ruth Rose return to Green Lawn to find another case waiting for them. "Mr. Bones", the school's skeleton, has disappeared from the nurse's office, and the entire school is tasked with tracking him down. Like the master sleuths they are, Dink, Josh, and Ruth Rose are on the case even before the announcement... but that reward sure would make their victory sweeter.
This time, there's a school full of suspects and a short series of clues to follow... but it turns out that this mystery is bigger than just, "where did Mr. Bones go"? It's a fun story a twist ending that's either unexpected or obvious, depending on how old you are when you read it; regardless, considering that most of the A to Z Mysteries plots are played completely straight, I think it's fairly clever and cute to have this one turn out to be an April Fool's Day prank.
I think it's one of the better mysteries in the second half of the series, and I definitely recommend it to young mystery readers. Fans of the Cam Jansen series, Capitol Mysteries series, kidlit Nancy Drew spin-offs, and all the other big mystery series for kids should definitely add this one to their reading queue.