At the latter hour a man had engaged his cab.  He had taken it to the side door of the restaurant, and the waiter had got in.  The man who hired the cab was already inside.

He had driven them somewhere on Fifty-seventh street, or it might be Fifty-eighth.  He couldn’t remember exactly.

The two men got out together.  He didn’t know what had become of them.

His fare was paid all right.  Then he had a couple more drinks, and the next thing he knew he was at the stable where he had hired the cab.

Of course he didn’t confess this in so many words, but Nick understood the facts well enough.

That was absolutely all that Harrigan knew about the case.

“Would you recognize the man who hired your cab if you saw him again?” asked Nick.

“Oh, sure,” said Harrigan.  “I wasn’t so very full.  I had me wits about me.  Say, you ain’t going to do me dirt an’ git me license taken away?  I was all right.  I didn’t do any harm.”

Nick assured Harrigan that if he acted right in this case his license would be safe, and then left the man to his slumbers.

“Not very promising, is it, my boy?” said Nick to Patsy, as they went downstairs.  “We’ve lost the trail as soon as we struck it.”

“Do you think he’s giving it to us straight?”

“Yes; he doesn’t know where he took the men nor what became of them after they left his cab.”

“It’s a pity he had such a jag.  He’d have been the best witness in the case.”

Nick smiled.

“If he hadn’t been drunk he wouldn’t have had anything to do with the case,” he said.

“What do you mean?”

“Why, it’s clear enough.  This man that we want saw Harrigan on that cab while the man was on his way to the restaurant with the woman.  Then when it became necessary to get Corbut out of the way, he remembered the drunken cabman, and hired him.”

“I don’t see how you know that.”

“A man would rather have a sober driver than a drunken one, wouldn’t he?”

“Yes.”

“Well, the man who told you he saw Harrigan get the job was sober, wasn’t he?”

“Yes.”

“Then why didn’t the man take his cab?  Because he wanted a drunken driver, who wouldn’t be sharp enough to get on to any queer business.

“But he wouldn’t have tried to find a drunken cabman just by luck, and he wouldn’t have taken a sober one.  Therefore he had seen Harrigan and hoped to find him in the same place.

“That’s part of the plot.  Now, then, you go to Chick, who’s watching the body of the woman.  I’m going to take Gaspard uptown and have a look at that part of the city where Harrigan left his passengers.”

Nick and Gaspard went to the Thirty-third street station of the Sixth avenue elevated road.

They walked to the edge of the platform on the uptown end.

Suddenly Gaspard gave a violent start.  He uttered an exclamation of surprise and pointed across the tracks.