Then her face went white as the concrete of the floor, and that was immaculate.  An expression which might have been fear, or horror, or hate—­or all three, spread over her features, transforming her.

Following the direction of her stare, I saw Shirley down the hall, just as he stopped at his own door.  He caught her glance suddenly, and his own face went red.  I thought that his hands trembled.

Marilyn wheeled about, lips pressed tightly together.  Throwing open the door, she dashed into her room, slamming it with a bang which echoed and re-echoed up and down the little hall.  She had forgotten our presence altogether.

XIV

ANOTHER CLUE

Kennedy looked at me quizzically.  “I guess we’d better not wait for Miss Loring to initiate us to McCann’s,” he remarked.

We found our way to the courtyard, and were headed for the gate when a young man in chauffeur’s cap and uniform intercepted us.  I had noticed him start forward from one of the cars parked in the inclosure, but did not recognize him.

“May I speak to you a moment, Professor Kennedy—­alone?”

“Mr. Jameson here is associated with me, is assisting me in this case, if it is something concerning the death of Miss Lamar.”

“It is, sir.  I saw you out at Tarrytown yesterday.  McGroarty is my name and I drove one of the cars the company went in.  They were pointing you out to me, and I’d read about you, and just now I says to myself there’s something I ought to tell you.”

“That’s right.”  Kennedy lighted a cigar, offering one to the chauffeur.  “I’m not supernatural and often I’m able to solve a mystery only with the help of all those who, like myself, want justice done.”

“Yes, sir!  That’s my way of looking at it.  Well”—­McGroarty blew a cloud of smoke, appreciatively—­“I do a good bit of driving for these people, and this morning it was cloudy and dull, no good for exteriors, but yet sort of so it might clear at any moment, and so I was ordered.  I brought my car and left it standing here in the yard while I went over to McCann’s—­the lunch room, you know—­for a cup of coffee.  When I came back”—­again the cigar—­ “there still was nothing doing, and so I thought—­you know how it is—­I thought I’d clean up the back of the old boat, to kill time, not saying it wasn’t needed.  So I took out the cocoa mat to beat it and what do I find on the floor—­between the mat and the rear seat it was, I guess—­but this.”

He handed Kennedy some small object which glinted in the light.  Looking closely, I saw that it was a peculiarly shaped little glass tube.

“An ampulla,” Kennedy explained.  “It’s the technical name the doctors have for such a container.”

“It must have been between the mat and the rear seat,” the chauffeur repeated.  Then he discovered that his cigar was out.  He struck a match.