"The one of which we found the envelope?" Bart inquired.

"That's the one. Well, these men evidently are mixed up in the case. It seems to concern property. Maybe Frank has some property and will not give it up."

"If Frank has any property he has a right to it!" said Fenn with emphasis. "Frank's done nothing wrong, but he certainly is acting queer."

"Then I don't know what to make of that reference to a sanitarium. They shut the door at that point and I couldn't hear any more."

The three boys discussed the subject from all sides, but could come to no solution of the mystery. That the men had referred to Frank, Ned was sure, and his chums partly agreed with him.

"Of course there are a number of boys named Frank," said Bart. "But when they spoke of Frank's uncle, Mr. Dent, it must be they meant our Frank."

"There's another thing," spoke Ned. "They mentioned pulling the wool over Mr. Dent's eyes. I wonder if we had better warn him."

"What could we tell him?" asked Fenn.

"I could tell what I heard," replied Ned.

"Which wouldn't be enough to do any good, and it might cause a lot of trouble," said Bart. "I think we'd better let this thing alone. Frank may tell us something that will give us an opening to talk to him about this matter, and you can then tell him what you heard the men say."

"I guess that's the best plan," admitted Ned.

"Perhaps we could learn something more of the men who were in the house,"

suggested Fenn.

"How?"

"By going down there and making inquiries. I know those buildings.

There's a watchman hired to stay on guard all night. Perhaps he saw the men and could tell us who they were."

"It's a good idea," said Ned. "We'll go down and see him to-morrow night.

That will be Sunday, and there's not likely to be any one around to hear us question him."

"We must not take Frank along," remarked Bart. "We'll have to keep this thing quiet from him, at least until we know more about it."

"It's the first time we haven't all been in a thing together," commented Ned. "It seems queer to have something on Frank doesn't know about."

"We're doing the best we know how," said Bart. "It's for Frank's interest we're working. I hope it will all come out right."

Sunday evening the three chums went to the building where Ned had been taken by the Upside Down boys. Frank had not called on any of his chums since the dinner the night before.

The boys found the night watchman, who had just come on duty. Ned knew him, for the man, James Rafferty, had once been employed as a porter in the bank of which Ned's father was cashier.

"Good evening, Mr. Rafferty," said Ned. "It's a fine night."

"It is that, me lad. An' what brings ye down here?"

"To see you."

"Sure, thin, an' ye must have some object. Few indade want's to see ould Rafferty now. He's gittin' too old fer much use."

"We wanted to ask if you saw anything of two strange men around these buildings last night?"

"Nary a wan did I see, Masther Ned. Sure there was a slatherin' lot of lads bint on some joke, an' I didn't interfere wid 'em, knowin' they was up t' no harm. But I saw no men."

"That blocks this end of the game," said Bart in a low tone, as he and his chums came away.

CHAPTER VI

FRANK GETS A LETTER

Somewhat disappointed at their failure to get any information from Rafferty, the three boys returned to Ned's house, where they had met that Sunday evening.

"Better let the thing drop until something turns up," suggested Bart. "We can't do anything, as I see."

"Only be on the lookout for strangers in town," said Ned. "I want to find out who those men were."

"And you'll have quite a job," spoke Bart. "I'm going home. See you at school to-morrow."

"There's one point we forgot to look up," Ned remarked.

"What is it?" inquired Fenn, as he prepared to accompany Bart.

"Those men spoke about someone being in a sanitarium. Do you know of any such place around here?"

"Never has been a sanitarium in this neighborhood," replied Bart.

"There's the hospital, but I don't believe they meant that."

"I either," responded Ned. "There's some mystery in it all. Perhaps we can solve it and help Frank."

Little was talked of at school next morning but the contest between the ball team members and the Upside Down Club. The story was told over again, with all sorts of embellishments, and there were any number of versions; from one that Ned had escaped by leaping from the roof, to another that his friends had descended on the building and torn it apart to get him out.

As a matter of fact the victory of the Upside Down society was only a partial one, as Ned had been able to go to the dinner before it was more than half over. The first-year lads had hoped to keep Ned a prisoner until the affair was at an end, but, it developed, there was a misunderstanding in the plans of the conspirators, and those boys who were supposed to be left to guard the prisoner, went away, giving Ned a chance to escape. But the contest with the older students gave the first-years chance enough to crow, and they lost no opportunity to do so.

"What'll we do to pay 'em back?" asked Ned of Bart at the noon recess.

"They're making all sorts of fun of us."

"Let 'em laugh. Our turn will come sooner or later."

Frank joined his chums that afternoon, when school had closed for the day, and all went swimming. There was quite a crowd of pupils at the river, including a number of the Upside Down boys, and there were several rather warm discussions among the members of the rival factions. Once or twice it looked as if there might be fights. Lem Gordon, in particular, was much incensed at the action of the first-years, and when Richard Kirk, a member of the Upside Down Club, taunted Lem with belonging to the side that lost in the Sat.u.r.day night struggle, Lem advanced toward Richard and acted as though he was going to strike him.

"Don't," advised Bart. "That will only make them keep the thing up longer. We'll fix 'em."

"We ought to do it pretty soon," growled Lem. "I'm getting tired of being laughed at. We ought to pay back the ringleaders anyhow. Who were the fellows that held you, Frank?"

"It was so dark I couldn't see well."