No one knows why Harry is wearing a necklace. Sidney thinks they're for girls. But when Harry opens the necklace cover to reveal a mini-microscope, the whole class is intrigued. Everyone wants to try it, so Harry promises to show them all some wicked-looking fungi at recess. But he doesn't mentiom that to see them they'll need to go outside the fence-and that means breaking a school rule. Will everyone follow him? What if Miss Mackle finds out? Has Harry gone too far this time?