The Black Sailor put his foot on the pedal of his bicycle. “You will excuse me if I break off this interesting conversation,” he said. “I have many things to attend to tonight, and it is getting late. But before I go I will give you this. It will serve to remind you that your meeting with me was not a trick of your imagination. It may also be useful as evidence of your veracity when you tell the story to the police.”

He drew something from his pocket, and threw it contemptuously at the Professor’s feet. Then, before the latter could reply, he had jumped on his bicycle and was pedaling rapidly in the direction from which he had come.