“It’s unlocked now,” said the physician grimly. “I was outside a moment ago.”
Oscar hurried downstairs to lock the front door. Doctor Lukens, his head bowed in thought, went into the room where Henry Marchand had died. He slumped into the chair before the desk.
It all seemed unreal. For a minute the physician believed that he had been the victim of hallucinations produced by the mental effort he had undergone in his study of the code.
Then his fingers fumbled in his vest pocket, and he brought out the card which the man in black had given him — the card which bore the telephone number to be called in an emergency.
Doctor Lukens smiled. Here was tangible evidence. This was a clew by which he might trace his visitor and learn the man’s identity.
Convinced of the reality of the situation, Doctor Lukens pondered deeply over the information which the man had given him. The logic of the stranger’s arguments had created a profound impression in the physician’s mind.
“It is true,” murmured Doctor Lukens. “True that my old friend Henry was murdered. This man has revealed the fact. Whoever he is — whatever he may be — he is ready to trace the murderer. I shall aid him as he wishes!”
The physician stared at the wall as his mind reverted to the mysterious man who had come to see him.
“Who can he be?” asked Doctor Lukens. “Where did he come from? Where did he go? It is unaccountable.” The physician pictured himself standing outside the front door, staring through the darkness.
“Strange!” he exclaimed. “He vanished as he appeared — like a living shadow!”