Seizing the round package and the tubing, he dashed out on the street and around the corner.  He tried the door opening into the Radium Corporation hallway.  It was closed, but unlocked.  As it yielded and we stumbled in, up the old worn wooden stairs of the building, I knew that there must be some one there.

A terrific, penetrating, almost stunning odor seemed to permeate the air even in the hall.

Kennedy paused at the door of the office, tried it, found it unlocked, but did not open it.

“That smell is ethyldichloracetate,” he explained.  “That was what I injected into the air cushion of that safe between the two linings.  I suppose my man here used an electric drill.  He might have used thermit or an oxyacetylene blowpipe for all I would care.  These fumes would discourage a cracksman from ‘soup’ to nuts,” he laughed, thoroughly pleased at the protection modern science had enabled him to devise.

As we stood an instant by the door, I realized what had happened.  We had captured our man.  He was asphyxiated!

Yet how were we to get to him?  Would Craig leave him in there, perhaps to die?  To go in ourselves meant to share his fate, whatever might be the effect of the drug.

Kennedy had torn the wrapping off the package.  From it he drew a huge globe with bulging windows of glass in the front and several curious arrangements on it at other points.  To it he fitted the rubber tubing and a little pump.  Then he placed the globe over his head, like a diver’s helmet, and fastened some air-tight rubber arrangement about his neck and shoulders.

“Pump, Walter I” he shouted.  “This is an oxygen helmet such as is used in entering mines filled with deadly gases.”

Without another word he was gone into the blackness of the noxious stifle which filled the Radium Corporation office since the cracksman had struck the unexpected pocket of rapidly evaporating stuff.

I pumped furiously.

Inside I could hear him blundering around.  What was he doing?

He was coming back slowly.  Was he, too, overcome?

As he emerged into the darkness of the hallway where I myself was almost sickened, I saw that he was dragging with him a limp form.

A rush of outside air from the street door seemed to clear things a little.  Kennedy tore off the oxygen helmet and dropped down on his knees beside the figure, working its arms in the most approved manner of resuscitation.

“I think we can do it without calling on the pulmotor,” he panted.  “Walter, the fumes have cleared away enough now in the outside office.  Open a window—­and keep that street door open, too.”

I did so, found the switch and turned on the lights.

It was Denison himself!

For many minutes Kennedy worked over him.  I bent down, loosened his collar and shirt, and looked eagerly at his chest for the tell-tale marks of the radium which I felt sure must be there.  There was not even a discoloration.