“All right!” Kennedy took the bag.  “Explain your marks so I’ll know—­” He stopped suddenly.  “No, don’t tell me anything.  I’ll make my chemical analyses and microscopic examinations without knowing the identity in the case either of the blood samples or the finger-nail files.  If I obtain results by both methods, and they agree, I’ll return armed with double-barreled evidence.  Meanwhile, Mackay, you get a smear from Miss Loring and follow us to the laboratory.  I’ll coax McGroarty to drive us down, so you’ll have your car and you can bring us back.”

The district attorney nodded.  “Me for McCann’s,” he muttered.  “That’s where she went to eat.”  He rushed off eagerly.

Kennedy had no difficulty persuading McGroarty to put his particular studio car at our disposal without an order from Manton or from the director who had called him.  In a very brief space of time we were at the laboratory.

“You expect to find the blood of one of those people showing traces of the antivenin?” I grasped Kennedy’s method of procedure, but wanted to make sure I understood it correctly.  Already I was blocking out the detailed article for the Star, the big scoop which that paper should have as a result of my close association with Kennedy on the case.  “One of those samples should correspond, I suppose, to the trace of blood on the portieres?”

“Exactly!” He answered me rather absently, being concerned in setting out the apparatus he would need for a hasty series of tests.

“Will the antivenin show in the blood after four, perhaps five days?”

“I should say so, Walter.  If it does not, by any chance, I will be able to identify the blood, but that is much more involved and tedious—­a great deal more actual work.”

“I’ve got it straight, then.  Now—­” I paced up and down several times.  “The finger-nail files should show a trace of the itching salve?  Is that correct, Craig?”

For a moment he didn’t answer, as his mind was upon his paraphernalia.  Then he straightened.  “Hardly, Walter!  The salve is soluble in water.  What I shall find, if anything, is some of the fibers of the towel.  You see, a person’s finger nails are great little collectors of bits of foreign matter, and anyone handling that rag is sure to show some infinitesimal trace for a long while afterward.  If the person stealing the towel filed or cleaned his nails there will be evidence of the fibers on his pocket knife or finger-nail file.  I impregnated the towel with that chemical so that I would be able to identify the fibers positively.”

“The use of the itching salve was unnecessary?”

A quizzical smile crept across Kennedy’s face.  “Did you think I expected some one to go walking around the studio scratching his hands?  Did you imagine I thought the guilty party would betray his or her identity in such childish fashion, after all the cleverness displayed in the crimes themselves?”