He hurried over to wash his hands.  I spread the towel out on the table and began to work in the stuff indicated by Kennedy.  There was no odor and it seemed like some patent ointment in color.  At first I was puzzled.  Then, absently, I touched the back of one hand with the greasy fingers of the other and immediately an itching set up so annoying that I had to abandon my task.

Kennedy chuckled.  “That’s itching salve, Walter.  The cuticle pads at your finger tips are too thick, but touch yourself anywhere else!—­” He shrugged his shoulders.  “You’d better use soap and water if you want any relief.  Then you can start over again.”

At the basin I thought I grasped his little plot.

“You’re going to plant the towel,” I asked, “so that the interested party will try to get hold of it?”

Evidently he thought it unnecessary to reply to me.

“Why couldn’t you just put it somewhere without all the preparation,” Mackay suggested, “and watch to see who came after it?”

“Because our criminal’s too clever,” Kennedy rejoined.  “Our only chance to get it stolen is to make it very plain that it is not being watched.  Whoever steals it, however, possibly will reveal himself on account of the itching salve.  In any case I expect to be able to trace the towel to the thief, no matter what efforts are made to destroy it.”

The towel was wrapped in a heavy bit of paper; then placed with a microscope and some other paraphernalia in a small battered traveling bag.  Climbing into Mackay’s little roadster, we soon were speeding toward the studio.

“Will you be able to help me, to stay with Jameson and myself all day?” Kennedy asked the district attorney, after perhaps a mile of silence.

“Surely!  It’s what I was hoping you’d allow me to do.  I have no authority down here, though.”

“I understand.  But the police, or an outsider, might allow some of my plans to become known.”  He paused a moment in thought.  “The film you brought in with you consists of the scenes on the rolls of negative in use at the time of Miss Lamar’s collapse.  It may or may not include the action where she scratched herself.  Now I want the scenes up to thirteen put together in proper order, first as photographed by one camera, then as caught by the other.  I’ll arrange for the services of a cutter, and for the delivery to me of any other negative or positive overlooked by us when we had the two boxes sealed and given into your custody at Tarrytown.  Will you superintend the assembly of the scenes, so that you can be sure nothing is taken out or omitted?”

“Of course!  I want to do anything I can.”