“That would do you no good,” Kennedy rejoined, “for we have no safe full of jewels for you to rob.  There are no keys to offices to be stolen from our pockets.  And let me tell you—­you are not the only man in New York who knows the secret of thermite.  I have told the secret to the police, and they are only waiting to find who destroyed Morowitch’s correspondence under the letter ‘P’ to apprehend the robber of his safe.  Your secret is out.”

“Revenge! revenge!” Poissan cried.  “I will have revenge.  Francois, bring out the jewels—­ha! ha!—­here in this bag are the jewels of Mr. Morowitch.  To-night Francois and I will go down by the back elevator to a secret exit.  In two hours all your police in New York cannot find us.  But in two hours you two impostors will be suffocated—­perhaps you will die of cyanogen, like Morowitch, whose jewels I have at last.”

He went to the door into the hall and stood there with a mocking laugh.  I moved to make a rush toward them, but Kennedy raised his hand.

“You will suffocate,” Poissan hissed again.

Just then we heard the elevator door clang, and hurried steps came down the long hall.

Craig whipped out his automatic and began pumping the bullets out in rapid succession.  As the smoke cleared I expected to see Poissan and Francois lying on the floor.  Instead, Craig had fired at the lock of the door.  He had shattered it into a thousand bits.  Andrews and his men were running down the hall.

“Curse you!” muttered Poissan as he banged the now useless lock, “who let those fellows in?  Are you a wizard?”

Craig smiled coolly as the ventilation cleared the room of the deadly cyanogen.

“On the window-sill outside is a selenium cell.  Selenium is a bad conductor of electricity in the dark, and an excellent conductor when exposed to light.  I merely moved my coat and hat, and the light from the furnace which was going to suffocate us played through the glass on the cell, the circuit was completed without your suspecting that I could communicate with friends outside, a bell was rung on the street, and here they are.  Andrews, there is the murderer of Morowitch, and there in his hands are the Morowitch—­”

Poissan had moved toward the furnace.  With a quick motion he seized the long tongs.  There was a cloud of choking vapour.  Kennedy leaped to the switch and shut off the current.  With the tongs he lifted out a shapeless piece of valueless black graphite.

“All that is left of the priceless Morowitch jewels,” he exclaimed ruefully.  “But we have the murderer.”

“And to-morrow a certified check for one hundred thousand dollars goes to Mrs. Morowitch with my humblest apologies and sympathy,” added Andrews.  “Professor Kennedy, you have earned your retainer.”

VII.  The Azure Ring

Files of newspapers and innumerable clippings from the press bureaus littered Kennedy’s desk in rank profusion.  Kennedy himself was so deeply absorbed that I had merely said good evening as I came in and had started to open my mail.  With an impatient sweep of his hand, however, he brushed the whole mass of newspapers into the waste-basket.