"You have to remember with whom you are dealing," Abbot Napp said, somewhat dejectedly. "The police commander, and my nephew are not trained in the use of logic. They are bureaucrats and soldiers; neither noted for their ability to think. You will find it very difficult to even explain what you have found, never mind convince them that it all means their favorite suspect is innocent. It cannot be done!"

Lindenthal agreed. "Just think, Brother Gregory, you will have to explain how the mud got into the fire grate and hearth. How you eliminated all other possible boots but those of the saboteur. How you then showed microscopically that there was pollen in the mud. How you showed that all pollen was different. How you showed where the other samples came from and how the Uzov road was the prime location. Then, last but not least, that Brother Matthew has hay fever triggered by Beifuss pollen - a medical fact that no one else acknowledges. I agree with Abbot Napp - no one will either believe or understand you!"

Even the optimistic Brother Gregory had to see the problem. "But at least it means we now know it was someone else who broke into the room and burnt the lists," he said with feeling. "All we have to do is find out who it was."

"Is that all," laughed Abbot Napp, bitterly. "You only have until Tuesday to do the impossible. It is one thing to know that someone else is responsible, it is another thing entirely to both find that person and prove beyond doubt that it was he."

"We must try!" shouted Brother Gregory. "We must try and find the real Hussite before it is too late."

Unfortunately the harder they tried, the less they succeeded and the Abbot left them a hour later no further forward than when they had started. He was cheered that Brother Matthew could be considered free of guilt, even if it was only in his own mind. The burden of his monk's possible involvement in this affair had been weighing on him quite heavily. At the very least he could now go to the tribunal and defend Brother Matthew with a free conscience.

"Perhaps if we found this mysterious observer," Lindenthal said, picking up the remains of Pech's parcel and going through its contents. "He must live around here, the food is wrapped in Thursday's edition of the Tagsbote newspaper. If the stamp is on it -- " he looked all over the pieces of newsprint, but found nothing. "Pity."

Mendel also looked at the package. "Who ever he was, he had a bad toothache," he said at last, holding up the remains of the root on which Pech had been chewing. "Also, these sandwiches were made by a woman, look at the way the bread has been cut and --" he paused to look closer at the bread and its contents. "This sandwich is made with bread from Terchova's bakery, look at the crust. Only bakery bread has crusts that thin."

Despite all their analysis, they could get no further than deciding that the mystery man was married, lived near a bakery and had a bad toothache. "Hardly a close description," said Lindenthal.

"But the porter may be able to add more," said Brother Gregory, "let's go and ask him." But their mission was interrupted by a small boy who brought an invitation.

"It's from Herr Rosenstrauch," Mendel told Lindenthal, "he has invited me over to his workshop tomorrow to continue our researches into optics."

"Will you go?" Brother Joseph asked. "Shouldn't we continue looking for clues?"

That was when Mendel remembered the contents of his handkerchief and a puzzling question that had been hidden at the back of his mind for some days now. "Yes," he said slowly, "but I think Herr Rosenstrauch may be able to provide our next clue, so let's take him up on his invitation. We may learn something to our benefit."