“What is it?” he demanded.  “Something, of course!  Aught new?”

For answer Chettle thrust his hand inside his overcoat and brought out a small package, wrapped in cartridge paper, and sealed.

He began to break the seals and unwrap the covering.

“Well, it brought me up here—­straight,” he said.  “I think I shall have to let our people at the yard know everything, Mr. Allerdyke.  But I came to you first—–­I only got to King’s Cross half an hour ago, and I drove on to you at once.  Well see what you think before I decide on anything.”

“What is it!” repeated Allerdyke, gazing with interest at the package.  “You’ve found something of fresh importance, eh!”

Chettle took the lid off a small box and produced Lydenberg’s watch and postcard on which the appointment in the High Street had been made.  He sat down at the table, laying his hand on the watch.

“After you left me this morning,” he said, “I started puzzling and puzzling over what had been discovered, what had been done, whether there was more that I could do.  I kept thinking things over all the morning, and half the afternoon.  Then it suddenly struck me—­there was one thing—­that I’d never done and that ought to have been done—­I don’t know why I’d never thought of it till then—­but I’d never had this photograph out of the watch.  And so I went back to the police-station and got the watch and opened it, and—­look there, Mr. Allerdyke!”

He had snapped open the case of the watch as he talked, and he now detached the photograph and turning it over, laid the reverse side down on the table by the postcard.

“Look at it!” he went on.  “Do you see?—­there’s writing on it!  You see what it says?  ‘This is J.A.  Burn this when made use of.’  You see?  And—­it’s the same handwriting as that on this card, making the appointment!  Here, look at both for yourself—­hold ’em closer to the light.  Mr. Allerdyke—­that was all written by the same hand, or I’m—­no good!”

Allerdyke went close to the electric globe above his dressing-table, the photograph in one hand, the postcard in the other.  He looked searchingly at both, brought them back, and laid them down again.

“No doubt of it, Chettle,” he said.  “No doubt of it!  It doesn’t need any expert to be certain sure of that.  The same, identical fist, without a shadow of doubt.  Well—­what d’ye make of it?  Here—­have a drink.”

He mixed a couple of drinks, pushed one glass to the detective, and took the other himself.

“Egad!” he muttered, after drinking.  “Things are getting—­hottish, anyway.  As I say, what do you make of this?  Of course, you’ve come to some conclusion?”

“Yes,” answered Chettle, taking up his glass and silently bowing his acknowledgments.  “I have!  The only one I could come to.  The man who sent this photograph to Lydenberg, to help him to identify your cousin at sight, is the man who afterwards lured Lydenberg into that part of Hull High Street, and shot him dead.  In plain words, the master shot his man—­when he’d done with him.  Just as he poisoned the Frenchwoman—­when he’d done with her.  Mr. Allerdyke, I’m more than ever convinced that these two murders—­Lydenberg’s and the French maid’s—­were the work of one hand.”