It was not until dusk that Nick Carter left the Gillespie house, and when he did so, it was on foot. He had not gone more than a block or so, however, before he hailed a passing taxi, and ordered the chauffeur to drive to a certain corner of Madison Avenue. The corner named was only a block from his own house.

Some hours had passed since Nick had read the letter which revealed the whereabouts of the real Chester J. Gillespie, but he had been in no hurry to act. For one thing, he wished to give the scoundrel a sense of security in this new and climax-capping adventure.

Nick was still disguised as Gillespie, but he was wearing a golf cap, which he had pulled down over his eyes, and a light overcoat, with upturned collar. His purpose was to get in touch with his assistant in one way or another, and his only anxiety concerned the possibility that Gordon had already got rid of Chick.

Fortunately, that was not the case, and, after a wait of no more than half or three-quarters of an hour, the young detective left the house, and unconsciously approached his chief, who was lounging at the corner.

As he passed Nick, the latter said quietly: “Go around the corner and wait for me.”

Chick stiffened slightly at the well-known voice, but that was the only sign of surprise he gave. With a grunt and a nod, he turned about at right angles into the side street, and along this Nick presently followed him.

A short distance beyond the corner, well out of sight from Nick’s house, Chick paused, and there his chief overtook him.

“I haven’t made any headway yet,” Chick announced, without any preliminaries. “I located the car late this afternoon, but there I came to a dead stop.”

“Never mind about that,” Nick said quickly. “It doesn’t matter in the least. I can lay my hands on Green-eye Gordon at any moment.”

“The deuce you can!” ejaculated Chick. “Then I should certainly say you don’t need me—for the sort of legwork I’ve been doing to-day, at any rate.”

“What about my double, though?” Nick put in swiftly, without giving Chick time to ask any questions. “Is he still at the house, and if so, what has he been doing?”

“He’s there, all right. He’s been writing letters in the bedroom. He declined to use the study.”

“Ah!” Nick murmured, in a peculiar tone. “Letters, eh? Has he mailed them?”

“No. I offered to do it for him a little while ago, but he said he would be going out himself later on.”

Nick thought over this information for a minute or two, while his assistant watched him questioningly.

“Did you happen to see any of the letters?” Nick inquired at length, rousing himself from his abstraction. “I mean, could you tell whether they were stamped or not?”

His assistant nodded. “I got a squint at a little pile of them,” he admitted. “The top one was stamped, but I could not say as to the rest.”

This required further thought on Nick’s part. He was tempted, of course, to end matters then and there, before those letters could reach their destination, and cause the consternation they were certain to create. On the other hand, he felt it necessary to give Gordon a little more leeway, and in order to do that, it seemed essential that the letters be mailed.

He had searched Gillespie’s private rooms, on the theory that Green Eye might have left the stolen papers there, but he had found nothing of the sort. Yet, it was imperative that these papers be recovered, if possible, at the same time the rascal was captured.

Unless that were done, the precious records might not be returned at all, for certainly Gordon could not be counted on to restore them voluntarily.

To be sure, the fact that he had been writing those letters—doubtless, blackmailing ones—under Nick’s own roof, suggested that he had the documents there to refer to. That, however, was by no means certain, for he might have put the records in some remote place, perhaps a safe-deposit vault, after making a list of the names and addresses desired.

Therefore, it seemed wise to give the fellow his head, for the time, and meanwhile to keep him under observation, in the hope that his movements would give some hint as to his possession or nonpossession of Nick’s papers.

The detective was about to explain this to his assistant when the latter broke in excitedly.

“For the love of Pete! What’s up?” he demanded. “What are you cooking up in that brain of yours, and why are you so curious about Gillespie’s doings?”

“Gillespie is down in South America,” Nick returned quietly. “That’s why. Our friend back there in the house is—well, you can guess, I imagine.”

And then he proceeded to give his instructions to the dumfounded Chick.