Approximately one-half hour later, a man walked leisurely up the street by the apartment house where Prokop lived. He disappeared outside the building.
A few minutes later he was in Prokop’s apartment. He was invisible there; only his flashlight betrayed his presence. He was searching, with infinite care.
His hand showed white beneath the light, as it discovered a small pad wedged behind a desk drawer.
The ray of the flashlight was centered on the pad. The fingers of the hand touched the surface of the top sheet of paper. Then the hand disappeared.
It came back, holding a small phial, filled with a black powder. It sprinkled the powder on the paper, and rubbed it into the surface.
Faint traces of writing appeared when the powder had been brushed away. The letters were followed by numbers. They gave the names and times of railway trains. The hand appeared with a folded sheet of paper, and opened it. A careful comparison was made.
The schedule which The Shadow had prepared by careful reasoning corresponded exactly with the one that he had found.
Prokop had written the list on the pad. He had torn off the top sheet. The impression had remained on the pad, which had dropped behind the desk drawer, when Prokop had put it away.
The Envoy had taken the actual list; the clew had remained.
The hand wrote on the list which had been prepared by deduction. It inscribed a single word: “Correct.” The figure disappeared from Prokop’s apartment.