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.