She had scarcely disappeared when, from the portiered doorway nearby, the Clutching Hand appeared, and, after gazing out at them, took a quick look at the safe.

“Good!” he muttered.

Noiselessly Michael of the sinister face moved in and took a position in the center of the room, as if on guard, while Clutching Hand sat before the safe watching it intently.

“Someone at the door—­Jennings is answering the bell,” Michael whispered hoarsely.

“Confound it!” muttered Clutching Hand, as both moved again behind the heavy velour curtains.

. . . . . . . .

“I’m so glad to see you, Mr. Kennedy,” greeted Elaine unaffectedly as Jennings admitted us.

She had heard the bell and was coming downstairs as we entered.  We three moved toward the library and someone switched on the lights.

Craig strode over to the safe.  The cold sweat on it had now turned to icicles.  Craig’s face clouded with thought as he examined it more closely.  There was actually a groaning sound from within.

“It can’t be opened,” he said to himself.  “The time lock is set for tomorrow morning.”

Outside, if we had not been so absorbed in the present mystery, we might have seen Michael and the Clutching Hand listening to us.  Clutching Hand looked hastily at his watch.

“The deuce!” he muttered under his breath, stifling his suppressed fury.

We stood looking at the safe.  Kennedy was deeply interested, Elaine standing close beside him.  Suddenly he seemed to make up his mind.

“Quick—­Elaine!” he cried, taking her arm.  “Stand back!”

We all retreated.  The safe door, powerful as it was, had actually begun to warp and bend.  The plates were bulging.  A moment later, with a loud report and concussion the door blew off.

A blast of cold air and flakes like snow flew out.  Papers were scattered on every side.

We stood gazing, aghast, a second, then ran forward.  Kennedy quickly examined the safe.  He bent down and from the wreck took up a package, now covered with white.

As quickly he dropped it.

“That is the package that was sent,” cried Elaine.

Taking it in a table cover, he laid it on the table and opened it.  Inside was a peculiar shaped flask, open at the top, but like a vacuum bottle.

“A Dewar flask!” ejaculated Craig.

“What is it?” asked Elaine, appealing to him.

“Liquid air!” he answered.  “As it evaporated, the terrific pressure of expanding air in the safe increased until it blew out the door.  That is what caused the cold sweating and the groans.”

We watched him, startled.

On the other side of the portieres Michael and Clutching Hand waited.  Then, in the general confusion, Clutching Hand slowly disappeared, foiled.

“Where did this package come from?” asked Kennedy of Jennings suspiciously.