“Hands off,” exclaimed Judy. “Stay away from our premises this evening, ladies, because we are going to try an experiment with explosives, and it might be dangerous.”

It was unfortunate that, on the very evening that Minerva Higgins had arranged to go to the three friends, somebody played a practical joke on her and she was in an extremely bad humor. Although she had regained her two medals, she was always losing things and crying her losses up and down the corridor. She usually found the articles mislaid in her own room, but she had a suspicious nature and was generally on the lookout for thefts. That afternoon she had rushed into the corridor crying:

“My water pitcher has been stolen from me. I will not have people going into my room and taking my things.”

“As if anybody wanted her old water pitcher,” remarked Margaret, in a tone of disgust.

Edith Williams smiled mysteriously.

Presently Minerva and the matron, much bored, passed the door.

“Come on, let’s go and see the fun,” suggested Edith.

“How do you know there will be any fun?” demanded Margaret.

“There’s likely to be.”

They strolled slowly up the corridor, and as they passed the door the matron was saying: