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.