"Now where does this come in?" he asked himself. "There isn't a grate in the house that has been touched for years. And this cake is not quite dry yet. And a bit of yellow soap in the tray over the sink that would be as hard as a chip if it had been here since the people left. But it hasn't. Murderer may have washed his hands, which is exceedingly likely, but what did he want blacklead for?"
Prout looked keenly around him. He opened the back door into a yard that gave on to a lane at the back of the house. The bricks were damp and mossy, and on them was something that looked like the print of wheels. The door leading to the lane was wide, and on the edge on both sides something patchy glistened. Prout touched it with his fingers.
"Now what does it mean?" he asked himself. "What game were they playing?"
The black edging of the gate-posts was fresh blacklead.
The little discovery gave a new twist to Prout's thoughts as he drove down to the National Credit Bank. He had no particular object save to see the manager and impress upon him that in the interests of justice the whole thing must be kept a profound secret. There was no difficulty about that: the cashier was indignant, for he had already given his promise on the matter.
"Not that you will ever see those notes again, sir," Prout said. "By this time they are probably on their way to the Continent, whence they may begin to dribble back one by one in the course of months. Still, one never can tell."
The manager was sympathetic; at the same time he looked at the clock, which was drawing very near to closing time. There was a lull outside in the traffic. Prout took up his hat and prepared to depart.
But the same moment his friend, the cashier, came rushing in. His eyes were gleaming behind his spectacles.
"A most extraordinary thing, sir," he stammered. "Those notes that Sergeant Prout came about just now are----"
"Get on," the manager said impatiently, "Get on."