"Well, Hugh, what do you think about that?" demanded Bob.

Hugh looked blankly at the rude drawing on the back of the envelope. "I don't know," he said slowly. "Why should they send Mr. Wernberg one of these?"

"Unless it's a message from one member of the gang to another."

"But Mr. Wernberg is in the hospital."

"The others may not know that."

"That's true," Hugh agreed. "This handwriting is the same as that on the messages that came to your father and to Heinrich too."

"I know it, and the same as in the list we found in the old house."

"What do you suppose the alligator stands for?"

"I've no idea. Why did they steal Percy?"

"Anyway we'd better ring the bell and deliver our message. We can't stand out here on the porch all day, you know."

Bob pushed the electric bell, and almost instantly the front door was opened by Frank Wernberg. It would seem as if he had been behind the door waiting all the time. His close-cropped light hair bristled fiercely, and his nose was still slightly swollen; his chin also was still raw where Bob had planted his fist the day before. Bob thought how much longer ago than that it seemed; so many things had happened in the last two days.

"What are you doing here?" demanded Frank brusquely.

Bob and Hugh had been so surprised by the sudden opening of the door that for a moment neither one of them replied.

"What do you want?" exclaimed Frank.

"We've got a letter for your mother," said Bob.

Frank glared at them under lowering brows. "Who from?" he asked.

"That's for her to find out," said Bob. "It's addressed to her you see."

Frank snatched the letter from Bob's outstretched hand, and made as if he was about to go in and shut the door.

"Wait a minute," exclaimed Hugh. "Here's another."

"What kind of a joke are you trying to play on me?" cried Frank angrily.

"None at all," said Hugh. "This one is for your father."

Frank grew red in the face, "If this is a joke I swear you'll be sorry for it," he exclaimed hotly.

"It's no joke at all," said Hugh. "We found this letter lying here under the mat. I was just going to hand it to you."

Frank took the letter from Hugh and looked at it suspiciously. Then he turned it over and looked at the back of it. Suddenly he turned pale.

Bob and Hugh, watching him closely, noticed this fact, and Bob, suddenly plucking up courage, determined to speak of it.

"What does that alligator mean, Frank?" he asked.

The color rushed back into Frank's face. He looked as though he were going to run. He swallowed hard two or three times, choked, and then swallowed again. "I don't know," he blurted out finally, and stepping inside slammed the door shut in the faces of the two boys.

Hugh looked at Bob and smiled. "Frank was certainly glad to see us, wasn't he?" he said sarcastically.

"I should say so," Bob agreed. "Let's go home."

They went down the steps and walked slowly in the direction of the
Cook home.

"Frank's a queer fellow," said Hugh finally.

"He certainly is," Bob agreed.

"Do you think he knows what has happened to his father?"

"I doubt it. I don't believe he would have been so surly if he had known."

"What do you think about the alligator?"

"I'm sure I don't know," said Bob. "It must mean something though, and
Frank must know what it is. Did you see how pale he got when he saw it!"

"Maybe it's the sign of some secret society like the Black Hand, or the
Ku Klux Klan, or something like that."

"Still I can't understand why they should send a warning to Mr. Wernberg if he is a member of the gang."

"It may not have been a warning," said Hugh. "Perhaps it was just a message of some kind or another."

"Then why should Frank have been so scared when he saw it?"

"Don't ask me. I'm getting more mixed up every minute."

They turned into the Cooks' yard and slowly approached the house. A man and woman were just disappearing around the corner.

"Who are they?" Hugh inquired.

"Lena, the cook, and one of her beaux," said Bob.

"I thought Heinrich was in love with her."

"He is," laughed Bob, "but he has a rival, and that's the man."

"What's his name?"

"Karl Hoffmann."

"Another German," said Hugh soberly.

"Say, Hugh," laughed Bob, "you certainly are suspicious. You suspect good old Lena, and now you suspect the man with her because he has a German name. Why, that man Hoffmann has worked for father for years, and father thinks the world of him."

"That doesn't mean he may not be mistaken," Hugh insisted.

"Why, father has even selected him as one of the guards for the factory," said Bob. "I guess that shows how much confidence he has in him."

"But suppose Lena is disloyal," exclaimed Hugh. "If Karl Hoffmann is in love with her there's no telling what she might get him to do."

"But Lena is not disloyal," said Bob peevishly. He was becoming tired of
Hugh's constant slurs against the people whom his father employed.

"Well, I'd watch them all," said Hugh.

Bob offered no further comment. He could not convince Hugh that his suspicions were unfounded so he decided there could be no use in arguing with him. They entered the house and found Mr. Cook seated in the library alone.

"Did you deliver my note?" he asked.

"We did," replied Bob.

"Who came to the door?"

"Frank," and Bob related their experiences to his father. Mr. Cook was much interested and puzzled by the manner in which Frank had acted when he saw the drawing of the alligator on the back of the envelope.

"We thought perhaps it might be the sign of some secret society," said Hugh.

"Possibly so," agreed Mr. Cook. "Let's see; the same sign was on the paper you found in the old house, Heinrich got a note with the picture on it, and now this letter you picked up on the Wernbergs' porch had it too."

"And the handwriting was the same as on that postal card you got this morning," said Bob.

"I didn't see any picture on that though."

"No," agreed Bob. "Neither did I."

"I threw the card away," said Mr. Cook. "I was afraid your mother might find it and worry."

"Perhaps there won't be any more trouble, now that Mr. Wernberg is out of the way," suggested Bob. "If he was the leader of the gang, his burns will keep him in the hospital and out of mischief for some time to come."

"You didn't hear what happened this afternoon then?" asked his father.

"No, what?" demanded Bob and Hugh in one breath.

"You remember the railroad bridge, don't you?"

"I guess we'll never forget that, will we, Hugh?" exclaimed Bob. "You don't mean that they tried to blow it up again?"

"Well, it looks so," said Mr. Cook. "One of the guards on the bridge this afternoon saw a man coming down the river in a rowboat. He called to him to halt, but the man kept right on. The guard challenged him three times, but as the man gave no answer he fired at him."

"Did he kill him?" demanded Bob excitedly.

"No," said Mr. Cook, "he didn't try to kill him. He just wanted to scare him, and when he fired the man jumped out of the boat into the water. The guard hurried down to the bank of the river, but the man had scrambled ashore and run off; you know it's quite a long distance from where the railroad tracks cross the bridge down to the water. The guard got a long pole and waded out into the river after the boat. He caught it finally and when he had hauled it ashore he found it was loaded with dynamite. Of course no one knows, but they think he planned to blow up the bridge."

"Whew!" exclaimed Hugh. "The man got away, you say?"

"Yes, unfortunately."

"Couldn't the guard see what he looked like?"

"Yes, he did see that, and here is the interesting part."

"What do you mean?"

"Why," said Mr. Cook, "the man was rather slight, weighing perhaps a hundred and fifty pounds and he had a close-cropped black mustache."

"The fake detective!" exclaimed Bob. "Was that who it was?"

"The description fits him, doesn't it?"

"Yes," agreed Hugh, "but he was out at the old house this afternoon. How could he be on the river at the same time?"

"He was out at the old house early this afternoon," said Mr. Cook. "This episode at the bridge happened only about an hour ago."

"He must have hurried right down there," exclaimed Bob. "When he realized that the police were on his trail he probably decided he had no time to lose, and that's why he dared try such a thing in broad daylight."

"Where did you hear about it, Mr. Cook?" inquired Hugh.

"Sergeant Riley just told me over the telephone; I had called him up to inquire how Mr. Wernberg was getting along."

"How is he?" asked Bob.

"Pretty bad yet; once in a while he recovers consciousness, but only for a few minutes. Besides he suffers so from his burns he can't do any talking."

"And meanwhile his gang keeps on working," said Hugh.

"Is that fake detective part of his gang?" said Bob. "He's the one who blew him up."

"I don't know," exclaimed Hugh in despair. "We just go 'round and 'round in circles and don't seem to get anywhere at all."

"But the fact remains, doesn't it, boys," inquired Mr. Cook, "that whether we know who the gang is, and what the relations are between the two gangs—if there are two—that somebody is hard at work plotting against this country? Also they are becoming bolder for they know that their time is short; sooner or later they are bound to be caught."

"You're afraid for your factory to-night, aren't you, father?" asked Bob.

"I am, indeed," said Mr. Cook.

Bob was on the point of asking if he and Hugh might not help guard it when the telephone rang and his father was called away to answer it.