"How?" interpolated Mr. Llewellyn John
"They obtained the guarantee."
"I remember," said Mr. Llewellyn John, "it was stolen."
"Mr. Dene used to leave his safe open with such papers in it as he wanted the enemy to see. That's what he meant when on one occasion he said, 'If you've got a hungry dog feed it.'"
Sir Bridgman North laughed, Sir Lyster turned to him reproachfully.
"Mr. Dene became convinced that an effort would be made to kidnap and hold him to ransom, the price being the plans of the Destroyer. Department Z. also became convinced of this, but at a later date. As a precaution John Dene sent to England by another ship his twin brother, known as James Grant. When everything was ready the two changed places; that accounted for the strangeness of manner that Miss West noticed with Mr. Dene a few days before his disappearance."
Malcolm Sage then went on to explain the method by which the false John Dene had been kidnapped, and of Department Z.'s discovery with relation to Mr. Montagu Naylor.
"But all that time what happened to the Destroyer?"
"The Destroyer was responsible for the extraordinary increase in the mortality among U-boats."
Mr. Llewellyn John jumped from his chair as if he had been thrown up by a hidden spring.