“Oh, he has a European fame, has he? Well, we’ve learned all about him in America. We know he is at the bottom of fifty murders, and yet we have nothing positive we can take him on. I tracked him over from New York, and I’ve been close to him for a week in London, waiting some excuse to get my hand on his collar. Mr. Gregson and I ran him to ground in that big tenement house, and there’s only one door, so he can’t slip us. There’s three folk come out since he went in, but I’ll swear he wasn’t one of them.”

“ Mr. Holmes talks of signals,” said Gregson. “I expect, as usual, he knows a good deal that we don’t.”

In a few clear words Holmes explained the situation as it had appeared to us. The American struck his hands together with vexation.

“He’s on to us!” he cried.