The headmaster interposed. “You must have made a mistake, Mr. Downing. There is certainly no trace of paint on this boot. These momentary optical delusions are, I fancy, not uncommon. Any doctor will tell you----” “I had an aunt, sir,” said Psmith chattily, “who was remarkably subject----” “It is absurd. I cannot have been mistaken,” said Mr. Downing. “I am positively certain the toe of this boot was red when I found it.” “It is undoubtedly black now, Mr. Downing.” “A sort of chameleon boot,” murmured Psmith. The goaded housemaster turned on him. “What did you say, Smith?” “Did I speak, sir?” said Psmith, with the start of one coming suddenly out of a trance. Mr. Downing looked searchingly at him. “You had better be careful, Smith.” “Yes, sir.” “I strongly suspect you of having something to do with this.” “Really, Mr. Downing,” said the headmaster, “that is surely improbable. Smith could scarcely have cleaned the boot on his way to my house. On one occasion I inadvertently spilt 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 boot. The afternoon sun, streaming in through the window, must have shone on the boot 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 boot. The picture on the retina of the eye, consequently, had not time to fade. I remember thinking myself, at the moment, that the boot appeared to have a certain reddish tint. The mistake----” “Bah!” 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 boot 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 boot with me, sir?” “If Mr. Downing does not want it?” The housemaster passed the fraudulent piece of evidence to Psmith without a word, and the latter, having included both masters in a kindly smile, left the garden.