"Really, Mr. Downing," said the headmaster, "this is surely improbable. Smith could scarcely have cleaned the shoe on his way to my house. On one occasion I inadvertently spilled some paint on a shoe of my own. I can assure you that it does not brush off. It needs a very systematic cleaning before all traces are removed."
"Exactly, sir," said Psmith. "My theory, if I may...?"
"Certainly Smith."
Psmith bowed courteously and proceeded.
"My theory, sir, is that Mr. Downing was deceived by the light-and-shade effects on the toe of the shoe. The afternoon sun, streaming in through the window, must have shone on the shoe in such a manner as to give it a momentary and fictitious aspect of redness. If Mr. Downing recollects, he did not look long at the shoe. The picture on the retina of the eye, consequently, had not time to fade. I remember thinking myself, at the moment, that the shoe appeared to have a certain reddish tint. The mistake...."
"Bag!" said Mr. Downing shortly.
"Well, really," said the headmaster, "it seems to me that that is the only explanation that will square with the facts. A shoe that is really smeared with red paint does not become black of itself in the course of a few minutes."
"You are very right, sir," said Psmith with benevolent approval. "May I go now, sir? I am in the middle of a singularly impressive passage of Cicero's speech De senectute."
"I am sorry that you should leave your preparation till Sunday, Smith. It is a habit of which I altogether disapprove."
"I am reading it, sir," said Psmith, with simple dignity, "for pleasure. Shall I take the shoe with me, sir?"