He bent down, took a knife from his pocket, and detached a tiny square of the mud with the impression of the broken tag in it. This he held in the palm of his hand, and continued. "All we've got to do now is to find who owns the pair of boots that'd make an impression like this. There can't be any mistake, and it shouldn't take us long to run through all the boots in the school."
"When?"
"To-night, when they're downstairs for cleaning. They are brought back by the boy about half-past five—if we get down to-night we'd be able to examine them safely."
"Good on you," said Jack, slapping Septimus on the back with heartiness. "I didn't think you could do it, but it's a good notion all the same. By George, we ought to be able to find out who it is!"
"But—who could it be?" asked Billy, a furrow of puzzlement showing itself on his forehead. "That's what gets me! I can't imagine—"
"The bootlace will show—don't worry," said Septimus. "We can't do anything until we find that."
The four of them were wondering, as they sat in class that afternoon, who the intruder could be, and they looked at their class-mates with suspicious eyes. Big Martin, on account of his size, came in for furtive glances, but it was manifestly absurd that he could have been the culprit.
At this early stage of the term, nobody felt much like work, particularly Septimus Patch, who always contrived to be doing as much of his own private business as possible, and never paid much attention to the lesson in hand. Just at this moment he had arranged a big barrier of books all along the front of his desk, and, concealed behind the screen, he was tinkering with a weir-looking model of many springs, screws, and cogwheels.
Consequently he did not notice that the boy in front of him had been surreptitiously unlacing his boots. His first intimation that something was amiss was when he felt a sharp tug at his feet, and both his boots came off. He gasped with horror, and, peering over his barricade, observed that his two boots were travelling the round of the class, in different directions. His loud socks, of purplish and yellow colour-scheme, brought a snigger from the class. He wriggled, protesting.
"Patch!" It was the voice of Mr. Salmon, who was all unconscious of the diversion, but who saw Patch's movement. "Are you paying attention?"