When Harry comes to school wearing a necklace, the whole class is intrigued. Harry opens the necklace and reveals a mini-microscope&150perfect for looking at the mold experiment Room 3B is working on! Everyone wants to try it, so Harry promises to show them a kingdom of mushrooms at recess. But there is one catch. They will have to go outside the playground fence, which means breaking a school rule. If they follow Harry, will they ever be able to face Miss Mackle again?