Muller waited outside， and his attention was attracted by a large grey Ulmer hound which was evidently waiting for some one within the shop. The dog came up to him in a most friendly manner， allowed him to pat its head， rubbed up against him with every sign of pleasure， and would not leave him even when he turned to go after Johann came out of the shop. Still accompanied by the dog， the two men walked on quite a distance， when a sharp whistle was heard behind them， and the dog became uneasy. He would not leave them， however， until a powerful voice called "Tristan！" several times. Muller turned and saw that Tristan's master was a tall， stately man wearing a handsome fur overcoat.
It was impossible to recognise his face at this distance， for the snowflakes were whirling thickly in the air. But Muller was not particularly anxious to recognise the stranger， as he had his head full of more important thoughts.
When Johann had given his new address and remarked that he would call for his coat soon， the men parted， and Muller returned to the police station.
The next day the principal newspaper of the town printed the following notice：
THE GOLDEN BULLET
It is but a few days since we announced to our readers the sad news of the death of a beautiful woman， whose leap from her window， while suffering from the agonies of fever， destroyed the happiness of an unusually harmonious marriage. And now we are compelled to print the news of another equally sad as well as mysterious occurrence. This time， Fate has demanded the sacrifice of the life of a capable and promising young man. Professor Paul Fellner， a member of the faculty of our college，was found dead at his desk yesterday morning. It was thought at first that it was a case of suicide， for doors and windows were carefully closed from within and those who discovered the corpse were obliged to break open one of the doors to get to it. And a revolver was found lying close at hand， upon the desk. But this revolver was loaded in every chamber and there was no other weapon to be seen in the room. There was a bullet wound in the left breast of the corpse， and the bullet had penetrated the heart. Death must have been instantaneous.
The most mysterious thing about this strange affair was discovered during the autopsy. It is incredible， but it is absolutely true， as it is vouched for under oath by the authorities who were present， that the bullet which was found in the heart of the dead man was made of solid gold. And yet，strange as is this circumstance， it is still more a riddle how the murderer could have escaped from the room where he had shot down his victim， for the keys in both doors were in the locks from the inside. We have evidently to do here with a criminal of very unusual cleverness and it is therefore not surprising that there has been no clue discovered thus far. The only thing that is known is that this murder was an act of revenge.
The entire city was in excitement over the mystery， even the police station was shaken out of its usual business-like indifference. There was no other topic of conversation in any of the rooms but the mystery of the golden bullet and the doors closed from the inside. The attendants and the policeman gathered whispering in the corners， and strangers who came in on their own business forgot it in their excitement over this new and fascinating mystery.
That afternoon Muller passed through Horn's office with a bundle of papers， on his way to the inner office occupied by his patron， Chief of Police Bauer. Horn， who had avoided Muller since yesterday although he was conscious of a freshened interest in the man， raised his head and watched the little detective as he walked across the room with his usual quiet tread. The commissioner saw nothing but the usual humble business-like manner to which he was accustomed - then suddenly something happened that came to him like a distinct shock. Muller stopped in his walk so suddenly that one foot was poised in the air. His bowed head was thrown back， his face flushed to his forehead， and the papers trembled in his hands. He ran the fingers of his unoccupied hand through his hair and murmured audibly， "That dog！ that dog！" It was evident that some thought had struck him with such insistence as to render him oblivious of his surroundings. Then he finally realised where he was， and walked on quickly to Bauer's room， his face still flushed， his hands trembling. When he came out from the office again， he was his usual quiet， humble self.
But the commissioner， with his now greater knowledge of the little man's gifts and past， could not forget the incident. During the afternoon he found himself repeating mechanically， "That dog - that dog." But the words meant nothing to him， hard as he might try to find the connection.
When the commissioner left for his home late that afternoon， Muller re-entered the office to lay some papers on the desk. His duties over， he was about to turn out the gas， when his eye fell on the blotter on Horn's desk. He looked at it more closely， then burst into a loud laugh. The same two words were scribbled again and again over the white surface， but it was not the name of any fair maiden， or even the title of a love poem； it was only the words， "That dog - "
Several days had passed since the discovery of the murder. Fellner had been buried and his possessions taken into custody by the authorities until his heirs should appear. The dead man's papers and affairs were in excellent condition and the arranging of the inheritance had been quickly done. Until the heirs should take possession， the apartment was sealed by the police. There was nothing else to do in the matter， and the commission appointed to make researches had discovered nothing of value. The murderer might easily feel that he was absolutely safe by this time.
The day after the publication of the article we have quoted， Muller appeared in Bauer's office and asked for a few days' leave.
"In the Fellner case？" asked the Chief with his usual calm， and Muller replied in the affirmative.
Two days later he returned， bringing with him nothing but a single little notice.
"Marie Dorn， now Mrs. Kniepp，" was one line in his notebook， and beside it some dates. The latter showed that Marie Dorn had for two years past been the wife of the Archducal Forest-Councillor， Leo Kniepp.
And for one year now Professor Paul Fellner had been in the town， after having applied for his transference from the university in the capital to this place， which was scarce half an hour's walk distant from the home of the beautiful young woman who had been the love of his youth.
And Fellner had made his home in the quietest quarter of the city， in that quarter which was nearest the Archducal hunting castle. He had lived very quietly， had not cultivated the acquaintance of the ladies of the town， but was a great walker and bicycle rider； and every Saturday evening since he had been alone in the house， he had sent his servant to the theatre. And it was on Saturday evenings that Forest-Councillor Kniepp went to his Bowling Club at the other end of the city， and did not return until the last train at midnight.
And during these evening hours Fellner's apartment was a convenient place for pleasant meetings； and nothing prevented the Professor from accompanying his beautiful friend home through the quiet Promenade， along the turnpike to the hunting castle. And Johann had once found a dog-whip in his master's room-and Councillor Leo Kniepp， head of the Forestry Department， was the possessor of a beautiful Ulmer hound which took an active interest in people who wore clothes belonging to Fellner.
Furthermore， in the little drawer of the bedside table in the murdered man's room， there had been found a tortoise-shell hairpin； and in the corner of the vestibule of his house， a little mother-of-pearl glove button， of the kind much in fashion that winter， because of a desire on the part of the ladies of the town to help the home industry of the neighbourhood. Mrs. Marie Kniepp was one of the fashionable women of the town， and several days before the Professor was murdered， this woman had thrown herself from the second-story window of her home， and her husband， whose passionate eccentric nature was well known， had been a changed man from that hour.
It was his deep grief at the loss of his beloved wife that had turned his hair grey and had drawn lines of terrible sorrow in his face - said gossip. But Muller， who did not know Kniepp personally although he had been taking a great interest in his affairs for the last few days， had his own ideas on the subject， and he decided to make the acquaintance of the Forest Councillor as soon as possible - that is， after he had found out all there was to be found out about his affairs and his habits.
Just a week after the murder， on Saturday evening therefore， the snow was whirling merrily about the gables and cupolas of the Archducal hunting castle. The weather-vanes groaned and the old trees in the park bent their tall tops under the mad wind which swept across the earth and tore the protecting snow covering from their branches. It was a stormy evening， not one to be out in if a man had a warm corner in which to hide.
An old peddler was trying to find shelter from the rapidly increasing storm under the lea of the castle wall. He crouched so close to the stones that he could scarcely be seen at all， in spite of the light from the snow. Finally he disappeared altogether behind one of the heavy columns which sprang out at intervals from the magnificent wall. Only his head peeped out occasionally as if looking for something. His dark， thoughtful eyes glanced over the little village spread out on one side of the castle， and over the railway station， its most imposing building. Then they would turn back again to the entrance gate in the wall near where he stood. It was a heavy iron-barred gate， its handsome ornamentation outlined in snow， and behind it the body of a large dog could be occasionally seen. This dog was an enormous grey Ulmer hound.
The peddler stood for a long time motionless behind the pillar， then he looked at his watch. "It's nearly time，" he murmured， and looked over towards the station again， where lights and figures were gathering.
At the same time the noise of an opening door was heard， and steps creaked over the snow. A man， evidently a servant， opened the little door beside the great gate and held it for another man to pass out. "You'll come back by the night train as usual， sir？" he asked respectfully.
"Yes，" replied the other， pushing back the dog， which fawned upon him.
"Come back here， Tristan，" called the servant， pulling the dog in by his collar， as lie closed the door and re-entered the house.
