"I don't know, Waldo," Ben said. "The whole school is under quarantine.
Plus, we're just kids. So how can we solve the mystery at Monster Academy?"
"I don't know yet," Waldo admitted.
"But what if it was my potion that caused the fog during the dance?"
His glasses slipped down his nose, and he pushed them back up.
"Maybe the fog from the lab traveled through the air vents to the gymnasium."
"Could be," Ben murmured, remembering the fog inside the lab.
"So you realize what this means, right?" said Waldo.
"The epidemic is all my fault!"
"It's not your fault, Waldo," Ben replied.
"If the flu was caused by the fog from the lab, then it's someone else's fault—the monster who ruined your experiment."
Waldo nodded, looking a little relieved. "Maybe you're right.
But sometime soon Mr. Freaky or the nurse will trace the flu back to the lab.
And then I'm in big trouble."
"Well, maybe we can try to find out who tampered with your experiment," said Ben.
"We could find the guilty monster and make him or her confess."
"That's what I was thinking too," said Waldo.
"First we have to figure out what we know—all the facts.
Then we can use those facts to figure out who our culprit is.
We know that there was fog in the lab."
"Another fact is that someone removed the hoses from your test tubes," Ben added.
"And we also know that purple fog filled the gym during the dance."
"Good," said Waldo.
"Here are some more things we know: both my potion and the fog were purple.
And now everybody in Monster Academy is purple."
"And nobody was sick before the dance," added Ben.
Suddenly Waldo's eyes lit up. "Actually, that's not true!
Miss Bungle has been sick since before the dance—before my potion caused that fog."
"You're right," said Ben thoughtfully. "I forgot about that.
Hey! Maybe your potion didn't cause this epidemic at all!"
Just then they heard voices.
They looked over the railing and saw Mr. Freaky at the bottom of the stairs.
The principal was with a tall human in a white coverall.
The man was wearing a mask and carrying a clipboard.
"That man must be the health inspector from People Place," Ben whispered.
"So you have no idea how this epidemic started?" the health inspector said to Mr. Freaky.
"No," said Mr. Freaky, wringing his hands.
"But trust me—I will find out what caused it.
Mayor Hubbletree has nothing to worry about.
Everything in Monster Academy is totally under control."
The health inspector sounded doubtful.
"It doesn't appear that things are totally under control here.
Everybody is purple. Nobody in People Place is purple.
Now, that's a place where things are totally under control."
Mr. Freaky took out his handkerchief and blew his noses.
"When did the epidemic start?" asked the health inspector.
"Who was the first person, er, monster to get sick?"
Mr. Freaky put away the handkerchief. "The first monster? Hmm, let's see . . .
That would be Miss Bungle, our broom-flying instructor."
Ben and Waldo looked at each other and smiled proudly.
The two of them had just remembered this fact.
"And where is she?" asked the health inspector.
"She's at home," said Mr. Freaky.
The health inspector made a note on his clipboard.
"Show me the cafeteria.
A lot of health problems occur where food is prepared.
I want to see what you monsters are cooking."
"Of course," said Mr. Freaky. "Follow me."
Waldo looked at Ben and grinned. "Whew!"
"I don't think you have anything to worry about, Waldo," said Ben.
"The health inspector will figure out what caused the epidemic, and then someone will find a cure." Ben sighed.
"I still have a problem though. Winnie's still mad at me."
"I'll help you explain things to her," Waldo offered.
"Come on, let's go find her right now."
Ben and Waldo went downstairs to look for Winnie.
As they passed through the lobby, a door opened, and in walked Miss Bungle!
The ogre who worked in the main office rushed into the lobby.
"Miss Bungle! You can't enter the building!
Monster Academy is under quarantine!"
The broom-flying teacher halted.
She looked quizzically at the office ogre, and then at Ben and Waldo.
"Why are you all . . . purple?"
"There's an epidemic. And a quarantine!" the ogre repeated.
"You have to leave at once!"
Waldo stared at Miss Bungle. "Wait a second," he murmured.
"Why are you surprised that we're all purple?
You've been sick with the flu all week. Didn't you turn purple too?"
Miss Bungle shook her head.
"No, I just had a minor case of monster flu—you know, sore throat, achy joints, and small green spots."