AT the remark Mr. Holton gasped in astonishment.

“Who would it be?” he asked. “Has anyone got anything against you?”

“Not that I know of,” Joe’s father replied. “Let me think.”

He assumed a mood of thoughtful anxiety, and Mr. Holton took the small box for a closer examination. It was about eight inches square, with a hole in the top out of which protruded a short iron stem. Inside, an alarm clock was still ticking.

“Hmm! That fire was probably set for ten o’clock,” Mr. Holton murmured, as he noticed that it was now nearly eleven.

“How long ago do you suppose it was set?” inquired Bob.

“Impossible to say,” the response came. “It couldn’t have been more than twelve hours ago, however.”

Mr. Lewis looked up.

“I can think of several people who could be bad enough to do this,” he said thoughtfully. “But I cannot say which one it would be.

“First I might mention a man who wanted to buy some specimens from me, but I declined to sell them. He had a sour disposition, and his temper was thoroughly aroused when, after he had offered large sums of money, I refused him. Said he’d get even some time.”

“What’d he want with them?” Joe asked.

“Wanted to sell them to a well-known museum. You see they were very rare birds that I got in New Zealand, and he’d have been offered a large sum for them.”

“Could be the very man!” Mr. Holton said. “Who else might have done it?”

“A rival naturalist,” the other returned. “Name is Davis—Thomas T. Davis. Perhaps you remember, Howard. The fellow with the gold eyeglasses and scarred face. Said he got it when a tiger sprang at him. Always——”

“Yes,” Mr. Holton interrupted, his eyes bright with sudden recollection. “The museum employed him awhile, didn’t it?”

Joe’s father nodded.

“He always had a dislike for me,” he went on. “Didn’t like it at all when I headed that expedition to central Asia.”

There was a short silence. Then Mr. Lewis made a resolution.

“I’m going to put this matter in the hands of detectives,” he said. “They may be able to figure it out.”

“That’s the thing to do,” Bob agreed. “Seems to me, though, that this first man you mentioned is responsible. The one who wanted to buy the specimens from you.”

“Could be. But I am very much in doubt as to whether he would do such a thing.”

“Are you certain that there is no one else that has anything against you?” Mr. Holton questioned.

“No. Not certain. But fairly sure.”

Suddenly Bob’s face lightened, and he turned to Mr. Lewis.

“Do you know where this man lives? The one who wanted to buy the specimens from you, I mean.”

“Why—yes,” Mr. Lewis faltered. “That is, I have it in my memorandum. What do you want with it?”

“Don’t know that it’ll be any good at all. But we could inquire of his neighbors what kind of man he is.”

“Good idea. Better let me go, though.”

Bob shook his head.

“Joe and I haven’t anything else to do,” he argued, “and we’ll be glad to do it.”

“All right. Come in the house and I’ll put his name and address on paper.”

In a short time Mr. Lewis was back with a folded paper, which he handed to Bob.

“Now use tact in getting your information,” he said. “Remember, don’t let the people you inquire of in on the secret.”

“We won’t,” came the response, and after securing permission to use Mr. Holton’s sedan, they left for the man’s address.

What would they find? Would the people living near know anything about this person? Would the youths find that he had moved and, owing to his criminal record, had told no one of his new location? These questions were in the minds of Bob and Joe as they went farther toward their destination.

After a twenty-minute ride they pulled up on a poor cross street near the city limits and gazed to their left at a small house set back from the sidewalk. Directly beside it was another house of slightly better appearance.

“That’s the place,” pronounced Bob. “Doesn’t look like anyone’s at home.”

“Let’s go to the house next to it,” suggested Joe, getting out of the car. “We’ll trust to luck that the occupants are not related to the man we’re after.”

The boys made their way to the door and knocked. For over a minute they waited in silence. Then, as it was evident that there was no one at home, they turned to leave. But at that moment a small car moved up to the curb and stopped. Two men got out and started toward the house where the alleged crook lived. But the second they caught sight of Bob and Joe they turned back to their car.

“Come on,” whispered Bob. “Let’s follow them. I have a notion that one of those fellows is the man we’re after.”

Joe nodded in agreement.

“Did you notice how strange they acted when they saw us?” he asked. “Perhaps they thought we were officers that had come to arrest them.”

The youths made their way to their automobile and had the motor started just as the other car whizzed away.

For over ten minutes they followed cautiously, and they were satisfied that the men had not noticed them. Then at last they turned up a dilapidated street and stopped in front of a small, weather-beaten house. Here they left the car and went inside, while Bob and Joe stopped a square away.

“Let’s go up and look around,” suggested Joe.

As quietly as possible, the boys walked up to the house.

“Come around to the back,” beckoned Joe. “There might be a window.”

His supposition proved correct, for they found one before they reached the back porch. The glass was out and the opening was boarded up fairly tight, but there were several large cracks.

Cautiously Bob leaned up close and peeped inside. Then he turned to Joe.

“Four men inside,” he whispered. “Two of them are the ones we followed. Wait! Let’s hear what they’re saying.”

Again he leaned over to the window, this time to listen. Joe squeezed up close that he might hear also.

“Where do you suppose he is?” one man was saying in a gruff voice.

“Left town, mebbe,” another answered. “Just plain slipped out on us, an’ him owin’ us a lot of dough.”

“The dirty tramp!” a third said with an oath. “We’ll get him, don’t you worry. No guy can put anything over on us!”

“He’s afraid of the cops, no doubt,” the first said. “Maybe—— But say! Speakin’ of cops, we saw a couple of guys at the house next door to him, and nobody lives there. Haven’t for two months. They might have been detectives.”

“He means us,” whispered Joe. “We scared them off, I guess.”

The man who had been silent now spoke.

“You may be right,” he said. “It don’t take them detectives long to get on a guy’s trail. If you stick around where you been keepin’ yourself they’ll get you sure. That’s prob’ly the reason why this guy ain’t home. Give him time. He’ll settle with us.”

But the first man was impatient.

“We want our dough now!” he bawled. “We was supposed to have it at noon an’ he didn’t come. He owes us a good many bucks, and for the spark machine too. He was supposed to pay for that, you know.”

Bob and Joe looked at each other. The spark machine!

“That proves it!” Bob whispered, gritting his teeth. “They’re the fellows that set your dad’s garage on fire, all right! We’ll make them——”

“Shhh!”

“But listen, Tim,” one of the men was saying, “there ain’t any use to get hot-headed yet. I know this guy pretty well. I’ve done a lot for him and he’s done a lot for me. He’s never backed out on me yet. He’s got plenty of money, even if he is tryin’ hard to get more.

“Here’s what let’s do. Let’s give him till tomorrow night, and then if he don’t pay us we can go after him.”

“All right.” And the agreement was made.

Bob and Joe looked at each other. What were they to do now? They had secured evidence that these men were the guilty ones. Now would it be best to report the matter to the police at once, or had they better wait longer for any further information that the crooks might unknowingly give them?

“Let’s wait a few more minutes,” suggested Joe. “They might leave the house just as we made for our car, and then it would be too bad.”

Bob thought this good advice, and he leaned against the house to wait. Joe remained at the window.

For a minute there was silence inside. Then the man called Tim got up from his chair and started for the door.

“Where you goin’?” he was asked.

“Over to see if I can’t collect that dough,” he growled. “Anybody want ter go with me?”

“What’s the use?” one fellow asked. “We was there not more than an hour ago.”

“All right. Leave it to me.”

He walked on toward the door.

“Come on,” muttered Joe. “Let’s get to our car before he gets away.”

As hastily, yet as quietly, as possible the youths ran around the back of the house and through the alley for a distance of about a square. Then they turned out to the street and to their car.

Joe had the motor started just as the crook left the curb.

“Let’s head him off,” suggested Bob. “We can easily get there before he does if we cut across and not take the through street.”

“Good idea,” and the car was turned up a narrow cross street.

Before long the boys were in the neighborhood of the house occupied by that man who had indirectly set Mr. Lewis’s garage on fire by hiring criminals experienced in that line to do it.

“Be careful and don’t get too close,” warned Joe, as they neared the structure.

“O. K. Let’s go around the alley. We can park there for a few minutes and nobody will know anything about it.”

The car was turned into the alley and parked almost directly behind the house. Then the youths got out to stretch their legs and decide on a plan of action.

“How will we work it?” asked Joe, glancing around to see if anyone happened to be watching them.

For a moment there was no answer. Then Bob had an idea.

“Let’s walk up to the back door,” he said. “There are a lot of trees and shrubbery close and we can hide behind them until we are sure that everything is all right.”

Joe agreed, and they made their way as quietly as possible.

When close enough, they saw that the door was shut and the blinds were drawn. It was evident that no one was at home.

Suddenly there came a noise from the front of the house and both boys concealed themselves behind a large clump of bushes.

“Someone’s coming around to the back door,” breathed Bob.

“Probably that’s Tim who came back here to collect the money owed him. The fellow we headed off, I mean. Yes, it’s he,” Joe observed, peeking down the side of the house.

The sound of footsteps grew louder, and the next minute the man stepped around the corner, fists clinched and face scowling.

“Come on,” said Bob, and leaving his place of hiding he launched himself with full force on the back of the crook.