Hal was astonished to learn from Katie McCabe that d.i.c.k Ferris was coming up the tenement stairs.

"He can't be coming here!" exclaimed the youth.

"What shall we do if he does?" asked McCabe.

"I don't know. Perhaps I had better hide. He may----"

At that instant came a knock on the door.

"It's him!" whispered Katie.

Andy McCabe, the father, pointed to a closet. Hal tiptoed his way to it, and motioned for Katie to follow. The door was closed, and then Andy McCabe answered the summons.

Ferris stood at the door, his hair disheveled and his lips trembling.

"May I ask who lives here?" he asked.

"My name is McCabe."

"Isn't there a man by the name of Macklin living here?" went on Ferris.

"Macklin?" repeated McCabe, slowly.

"Yes, Tommy Macklin."

"Not as I know on. What does he do?"

"I don't know. I have a letter to deliver to him. So you don't know where he lives?"

"No, sir."

"It's too bad. Will you please tell me what time it is?"

Andy McCabe glanced at the alarm clock that stood on the mantel-shelf.

"Quarter to six."

"As late as that!" cried Ferris. "I must hurry and catch him before six.

Only quarter of an hour. Good-day, sir."

"Good-day."

In a moment Ferris was gone. McCabe closed the door, and Hal came out of the closet followed by Katie.

"What does he mean?" questioned the man.

"I'll tell you what it means," said Hal. "He is trying to prove an alibi, in case a body was found in the vat. He thinks you can remember he was here looking for Macklin at quarter to six. If that was true, how could he have helped Macklin at five o'clock?"

"Well, well! he's a smart villain, so he is!" exclaimed Andy McCabe. "I wonder what he would have done if you had stepped out of the closet?"

"I was strongly tempted to do that," laughed Hal. "But now I must be off, Mr. McCabe. Please keep quiet, as I told you."

"I will, Mr. Carson. But where be you going?"

"To follow Ferris. Say, have you an old slouch hat you will exchange for this cap of mine?"

"Here is one of Jack's."

"That will do first-rate."

Hal put on the hat and drew it down over his brow.

"Going to turn spy, be you?" remarked Andy McCabe.

"Yes."

"Well, I wish you luck."

Hal was soon out of the house. Once in the street, he looked up and down.

Ferris was not in view, but he soon caught sight of the fellow coming out of a tenement across the way. He crossed over and followed Ferris toward Park Row, and then to the boarding house.

Here Hal heard the youth say something to his aunt about changing his clothing, and the boy slipped into the house un.o.bserved by anyone, and did likewise. Ferris then left again, followed by Hal.

"I suppose he thinks he has laid good ground-work for his alibi,"

thought Hal. "Well, let him think so, he will be surprised before long to learn the truth."

At Fourteenth Street d.i.c.k Ferris turned and walked toward Broadway. Hal followed close behind, but in the crowd at the corner he lost track of the fellow he was after.

He looked this way and that, and into the restaurants, but Ferris had disappeared.

What was to do next? It was past supper-time, but Hal was in no humor for eating.

Suddenly somebody brushed him rudely. It was a man wearing a heavy cape coat. Hal glanced at the individual sharply, and was astonished to see it was Mr. Caleb Allen.

Allen had not seen Hal, and the boy at once placed himself where he was not likely to be noticed.

"I wonder if he and Ferris met?" thought Hal. "It isn't likely, but yet it may be so. The three of them are into this, and so is that fellow Macklin. I must be careful, and keep my eyes wide open."

Allen pa.s.sed up Union Square on the west side, and Hal made it a point to follow close behind.

Arriving at Seventeenth Street, Allen turned down toward the North River. He pa.s.sed over several blocks, and finally ascended the steps of a small mansion on the left.

The front of the mansion was totally dark, but when the door was opened Hal saw that the interior was brilliantly illuminated.

As soon as Allen pa.s.sed in the door was closed, and all became as dark as before, Hal hesitated, and then ascending the steps, looked for a door-plate.