"There will be a nice little surprise party for some one at bedtime," he said to himself, but did not let his satisfaction show on his face, so that for all that appeared no one knew of the little trick.

He had had his own flashlight with him and had not had to turn up the lights in the dormitory, a proceeding that might have caused attention, and he was sure that no one had seen him at work, and indeed no one had.

When the boys went up to bed, Jack, still occupying the same dormitory as at first, Billy was ready to see the result of his little joke, but said nothing to any of the boys about it.

"Will you change beds with me to-night, Billy?" presently asked Jack, taking off his coat and hanging it on a hook. "Mine is a little too warm, but you don't mind that."

"Now I wonder if he has got onto it?" thought Billy. "He could not have been up here since."

"It will only be for to-night," Jack added.

"What's the use of changing?" asked Billy. "I don't like too warm a bed myself."

"Oh, this isn't too warm, just warm enough for you," laughed Jack.

"He has got onto something," thought Billy, "and wants to see me go down. Not much, I won't."

"Why can't you be obliging, Billy?" asked Arthur. "I'm sure I'd do a little thing like that if I was asked."

"I wonder if they are both in it?" thought the young joker.

"Oh, well, it doesn't matter," said Jack, taking off his waistcoat and hanging it up over his coat.

"You can have my bed if you want it, Jack," said Arthur. "I don't see why Billy is so disobliging."

"Well, I did not mean it for him," thought Billy, "but it will be his own fault if he makes the change."

"Billy's is better," laughed Jack, "but still I don't mind changing with you if you don't object."

"Not in the least," said Arthur. "You're an obliging fellow, Mr. William Manners."

"Very bad manners, I should say," laughed Harry.

"Oh, well, I am a bit particular, I suppose," said Billy, "but I get accustomed to a thing and don't like to change. It's the same with a seat at table or a desk in the schoolroom."

Billy had been in a hurry to get ready for bed in case the boys tried to persuade him to change his mind, and now he threw back the covers and plumped himself in without further delay.

In a moment there were several surprises.

First, the bed went all to pieces and let the rather stout young fellow down upon the floor in the most unceremonious fashion.

Then there was a loud report, as if a pistol had been set off, and a lot of smoke puffed up in Billy's face.

Next the washstand tipped over and Billy received a ducking much worse than he had got on the night that Jack's water pitcher had been overturned upon him.

"h.e.l.lo! what's the matter with Billy?" asked several of the boys.

"Oh, you prefer that sort of bed, do you?" asked Arthur.

"Maybe that is why he did not want to let Jack have it," added Harry.

"Enjoy yourself, Billy," said Jack with a smile, sitting on his own bed.

Nothing happened, much to Billy's surprise and disappointment.

"How is this?" the joker asked as he got up. "Did I fix the wrong bed, after all?"

"No, that was all right, Billy, but I have been here since," laughed Jack, taking off his socks.

"Huh! And you found it out?"

"Quite so!" with another smile.

"How did you do it? Sit on it?"

"No, but you left the end of a string sticking out."

"How do you know I did it?" asked Billy.

"Because you are the only fellow that uses green cord in tying up parcels. I have noticed that, among other things."

"Billy is a bit green himself when it comes to playing jokes on observant boys," remarked Harry.

"But how did you happen to come up here ahead of time?" asked Billy, paying no attention to Harry's observation.

"Accident, that's all. I wanted something."

"But I did not see you leave the room," said Billy. "You did not see me at work?"

"No, but I saw you come in. Even then I did not suspect anything. I was about to go up when you came in."

"And then you fixed my bed?" with a grunt.

"Certainly. What is good enough for me is equally good for you, isn't it, my boy?"

"Yes, but, Jack, you offered to swap beds with him," chuckled Arthur.

"To be sure. I knew he would not take me up."

"And if he had?"

"Well, my side of the joke would have been off, but I would not have sat on the bed."

"Well, but what was the racket?" asked Billy.

"Giant torpedo under the bed," said Jack. "That was an improvement on your invention."

"Well, that's one on you!" said Harry with a broad grin.