his box down the street, understood from it that he was to move slowly along behind Mr. Birnes, and be prepared for an emergency.

Half-way between Thirty-third and Thirty-fourth Streets, Jerry Malone approached and passed Mr. Wynne without so much as a glance at him, and went on toward his chief.

"Drop in behind here," Mr. Birnes remarked crisply to Malone, without looking around. "I'll walk on ahead and turn east in Thirty-fourth Street to nail him if he swings a car. Claflin's got him going west."

Mr. Wynne was perhaps some twenty feet from the corner of Thirty-fourth Street and Fifth Avenue when Mr. Birnes passed him. His glance lingered on the broad back of the chief reflectively as he swung by and turned into the cross street, after a quick, business-like glance at an approaching car. Then Mr. Wynne smiled. He paused on the edge of the curb long enough for an automobile to pass, then went on across Thirty-fourth Street to the uptown side and, turning flatly, looked Mr. Birnes over pensively, after which he leaned up against an electric-light pole and scribbled something on an envelope.

A closed cab came wriggling and squirming up Fifth Avenue. As it reached the middle of Thirty-fourth Street Mr. Wynne raised his hand, and the cab drew up beside him. He said something to the driver, opened the door and stepped in. Mr. Birnes smiled confidently. So that was it, eh? He, too, crossed Thirty-fourth Street and lifted his hand. The cab which had been drifting along behind him immediately came up.

"Now, Jimmy, get on the job," instructed Mr. Birnes, as he stepped in. "Keep that chap in sight and when he stops you stop."

Mr. Wynne's cab jogged along comfortably up the avenue, twisting and winding a path between the other vehicles, the while Mr. Birnes regarded it with thoughtful gaze. Its number dangled on a white board in the rear; Mr. Birnes just happened to note it.

"Grand Central Station, I'll bet a hat," he mused.

But the closed cab didn't turn into Forty-second Street; it went past, then on past Delmonico's, past the Cathedral, past the Plaza, at Fifty-ninth Street, and still on uptown. It was not hurrying— it merely moved steadily; but once free of the snarl which culminates at the Fifty-ninth Street entrance to Central Park, its speed was increased a little. Past Sixty-fourth Street, Sixty-fifth, Sixty-sixth, and at Sixty-seventh it slowed up and halted at the sidewalk on the far side.

"Stop in front of a door, Jimmy," directed the detective hastily.

Jimmy obeyed gracefully, and Mr. Birnes stepped out, hardly half a block behind the closed cab. He went through an elaborate pretense of paying Jimmy, the while he regarded Mr. Wynne, who had also alighted and was paying the driver. The small sole-leather grip was on the ground between his feet as he ransacked his pocketbook. A settlement was reached, the cabby nodded, touched his horse with his whip and continued to jog on up Fifth Avenue.

"Now, he didn't order that chap to come back or he wouldn't have paid him," the detective reasoned. "Therefore he's close to where he is going."

But Mr. Wynne seemed in no hurry; instead he stood still for a minute gazing after the retreating vehicle, which fact made it necessary for Mr. Birnes to start a dispute with Jimmy as to just how much the fare should be. They played the scene admirably; had Mr. Wynne been listening he might even have heard part of the vigorous argument. Whether he listened or not he turned and gazed straight at Mr. Birnes until, finally, the detective recognized the necessity of getting out of sight.

With a final explosion he handed a bill to Jimmy and turned to go up the steps of the house. He had no business there, but he must do something.

Jimmy turned the cab short and went rattling away down Fifth Avenue to await orders in the lee of a corner a block or so away. And, meanwhile, as Mr. Wynne still stood on the corner, Mr. Birnes had to go on up the steps. But as he placed his foot on the third step he knew—though he had not looked, apparently, yet he knew—that Mr. Wynne had raised his hand, and that in that hand was a small white envelope. And further, he knew that Mr. Wynne was gazing directly at him.

Now that was odd. Slowly it began to dawn upon the detective that Mr. Wynne was trying to attract his attention. If he heeded the signal—evidently it was intended as such—it would be a confession that he was following Mr. Wynne, and realizing this he took two more steps up. Mr. Wynne waved the envelope again, after which he folded it across twice and thrust it into a crevice of a water-plug beside him. Then he turned east along Sixty-seventh Street and disappeared.

The detective had seen the performance, all of it, and he was perplexed. It was wholly unprecedented. However, the first thing to do now was to keep Mr. Wynne in sight, so he came down the steps and walked rapidly on to Sixty-seventh Street, pausing to peer around the corner before he turned. Mr. Wynne was idling along, half a block away, without the slightest apparent interest in what was happening behind. Inevitably Mr. Birnes' eyes were drawn to the water-plug across the street. A tag end of white paper gleamed tantalizingly. Now what the deuce did it mean?

Being only human, Mr. Birnes went across the street and got the paper. It was an envelope. As he unfolded it and gazed at the address, written in pencil, his mouth opened in undignified astonishment. It was addressed to him—Steve Birnes, Chief of the Birnes Detective Agency. Mr. Wynne had still not looked back, so the detective trailed along behind, opening the envelope as he walked. A note inside ran briefly:

   My address is No. —— East Thirty-seventh Street. If it is
   necessary for you to see me please call there about six o'clock
   this afternoon.
   E. VAN CORTLANDT WYNNE

Now here was, perhaps, as savory a kettle of fish as Mr. Birnes had ever stumbled upon. It is difficult to imagine a more embarrassing situation for the professional sleuth than to find himself suddenly taken into the confidence of the person he is shadowing. But was he being taken into Mr. Wynne's confidence? Ah! That was the question! Admitting that Mr. Wynne knew who he was, and admitting that he knew he was being followed, was not this apparent frankness an attempt to throw him off the scent? He would see, would Mr. Birnes.

He quickened his pace a little, then slowed up instantly, because Mr. Wynne had stopped on the corner of Madison Avenue, and as a downtown car came rushing along he stepped out to board it. Mr. Birnes scuttled across the street, and by a dexterous jump swung on the car as it fled past. Mr. Wynne had gone forward and was taking a seat; Mr. Birnes remained on the back platform, sheltered by the accommodating bulk of a fat man, and flattered himself that Mr. Wynne had not seen him. By peering over a huge shoulder the detective was still able to watch Mr. Wynne.

He saw him pay his fare, and then he saw him place the small sole-leather grip on his knees and unfasten the catch. Not knowing what was in that grip Mr. Birnes was curious to see what came out of it. Nothing came out of it—it was empty! There was no question of this, for Mr. Wynne opened it wide and turned it upside down to shake it out. It didn't mean anything in particular to Mr. Birnes, the fact that the grip was empty, so he didn't get excited about it.

Mr. Wynne left the car at Thirty-fourth Street, the south end of the Park Avenue tunnel, by the front door, and the detective stepped off the rear end. Mr. Wynne brushed past him as he went up the stairs, and as he did so he smiled a