"I don't think we need bother about the back part of the house for the present," Robinson said. "Howells's
evidence has been stolen. It's your job to find it unless it's been destroyed. Your other job is to discover the
instrument that caused death in both cases. Then maybe our worthy doctor will desert his ghosts. Mr.
Blackburn, if you will come with me there's a slight possibility of checking up some of the evidence of which
Howells spoke. Our fine fellow may have made a slip in the court."
Bobby understood and was afraid--more afraid than he had been at any time since he had overheard Howells
catalogue his case to Graham in the library. Why, even in so much confusion, had Graham and he failed to
think of those tell-tale marks in the court? They had been intact when he had stood there just before dark. It
was unlikely any one had walked across the grass since. He saw Graham's elaborate precautions demolished,
the case against him stronger than it had been before Howells's murder. Graham's face revealed the same
helpless comprehension. They followed Robinson downstairs. Graham made a gesture of surrender. Bobby
glanced at Paredes who alone had remained below. The Panamanian smoked and lounged in the easy chair.
His eyes seemed restless.
"I shall wish to ask you some questions in a few minutes, Mr. Paredes," the district attorney said.
"At your service, I'm sure," Paredes drawled.
He watched them until they had entered the court and closed the door. The chill dampness of the court
infected Bobby as it had always done. It was a proper setting for his accusation and arrest. For Robinson, he
knew, wouldn't wait as Howells had done to solve the mystery of the locked doors.
Robinson, while the others grouped themselves about him, took a flashlight from his pocket and pressed the
control. The brilliant cylinder of light illuminated the grass, making it seem unnaturally green. Bobby braced
himself for the inevitable denouement. Then, while Robinson exclaimed angrily, his eyes widened, his heart
beat rapidly with a vast and wondering relief. For the marks he remembered so clearly had been obliterated
with painstaking thoroughness, and at first the slate seemed perfectly clean. He was sure his unknown friend
had avoided leaving any trace of his own. Each step in the grass had been carefully scraped out. In the
confusion of the path there was nothing to be learned.
The genuine surprise of Bobby's exclamation turned Robinson to him with a look of doubt.
"You acknowledge these footmarks were here, Mr. Blackburn?"
"Certainly," Bobby answered. "I saw them myself just before dark. I knew Howells ridiculously connected
them with the murderer."
"You made a good job of it when you trampled, them out," Robinson hazarded.
But it was clear Bobby's amazement had not been lost on him.
"Or," he went on, "this foreigner who advertises himself as your friend! He was in the court tonight. We know
that."
Suddenly he stooped, and Bobby got on his knees beside him. The cylinder of light held in its centre one
mark, clear and distinct in the trampled grass, and with a warm gratitude, a swift apprehension, Bobby thought
of Katherine. For the mark in the grass had been made by the heel of a woman's shoe.
"Not the foreigner then," Robinson mused, "not yourself, Blackburn, but a woman, a devoted woman. That's
something to get after."