The little General Passenger Agent looked pleased and smoothed his beautiful whiskers softly.
"I was most happy," said he.
"Just now," said Ashton-Kirk, "I am engaged in a matter of some consequence, and once more you can be of assistance to me."
"Sit down," invited the other, readily. "Sit down, and command me."
Both Pendleton and the investigator sat down. The latter said to the passenger agent:
"I understand that every railroad has a system by which it can tell which conductor has punched a ticket."
"Oh, yes. A very simple one. You see the hole left by each punch is different. One will cut a perfectly round hole, another will be square, still another will be a triangle, and so on, indefinitely."
From his card case, Ashton-Kirk produced the small red particle which he had found upon the desk of the murdered man.
"Here is a fragment cut from a ticket," he said. "It is shaped like a keystone. I should like to know, if you can tell me, what train is taken out by the conductor who uses the keystone punch."
The agent touched a signal and picked up the end of a tube.