“Let me see.  It is now four o’clock.  If you can get hold of all these people in time I think I shall be ready for the final scene to-night—­say, at nine.  You know how to arrange it.  Have them all present at my laboratory at nine, and I promise we shall have a story that will get into the morning papers with leaded type on the front page.”

“Now, Walter,” he added, as we hurried down to the taxicab again, “I want you to drop off at the Department of Health with this card to the commissioner.  I believe you know Dr. Leslie.  Well, ask him if he knows anything about this Bridget Fallon.  I will go on up-town to the laboratory and get my apparatus ready.  You needn’t come up till nine, old fellow, for I shall be busy till then, but be sure when you come that you bring the record of this Fallon woman if you have to beg, borrow, or steal it.”

I didn’t understand it, but I took the card and obeyed implicitly.  It is needless to say that I was keyed up to the greatest pitch of excitement during my interview with the health commissioner, when I finally got in to see him.  I hadn’t talked to him long before a great light struck me, and I began to see what Craig was driving at.  The commissioner saw it first.

“If you don’t mind, Mr. Jameson.” he said, after I had told him as much of my story as I could, “will you call up Professor Kennedy and tell him I’d like very much to be present to-night myself?”

“Certainly I will,” I replied, glad to get my errand done in first-class fashion in that way.

Things must have been running smoothly, for while I was sitting in our apartment after dinner, impatiently waiting for half-past eight, when the commissioner had promised to call for me and go up to the laboratory, the telephone rang.  It was Craig.

“Walter, might I ask a favour of you?” he said.  “When the commissioner comes ask him to stop at the Louis Quinze and bring Miss Bisbee up, too.  Tell her it is important.  No more now.  Things are going ahead fine.”

Promptly at nine we were assembled, a curious crowd.  The health commissioner and the inspector, being members of the same political party, greeted each other by their first names.  Miss Bisbee was nervous, Bridget was abusive, Denny was sullen.  As for Kennedy, he was, as usual, as cool as a lump of ice.  And I—­well, I just sat on my feelings to keep myself quiet.

At one end of the room Craig had placed a large white sheet such as he used in his stereopticon lectures, while at the top of the tier of seats that made a sort of little amphitheatre out of his lecture-room his stereopticon sputtered.

“Moving pictures to-night, eh?” said Inspector O’Connor.

“Not exactly,” said Craig, “though—­yes, they will be moving in another sense.  Now, if we are all ready, I’ll switch off the electric lights.”

The calcium sputtered some more, and a square of light was thrown on the sheet.