When he arrived at the top of the hill, he found the two strangers, as he had expected, sitting at a little table outside the building.
'Hallo, youngster, have you caught your swallow-tail yet?' inquired the tall one.
'I have not even seen one,' replied Franz, truthfully. 'I am afraid they have all left the Hirsch-felsen since you were there. I gave it up at last and came on here to send a cypher telegram to my friend.'
'Ah! the cypher!' said the fat man. 'Show me what you are going to say, and I will warrant myself to read it.'
'Very well, but be quick, for I want to send it off,' replied Franz, seeing that this would disarm suspicion.
He gave the strangers the copy he had specially prepared for them, and, to his surprise, the stout man did manage to read it, though, naturally, he thought nothing of its contents. Then Franz took the real telegram to the clerk at the Observatory, who dispatched it carefully, though he chaffed Franz a good deal about the enormous importance of a message that required to be sent so secretly.
When he rejoined his companions by the lake, just in time for the afternoon meal, he was well teased by them because he was the only boy who had no important find to announce. Then followed a merry walk back through the woods, then supper, and then bed, and through it all Franz never had a chance of a private talk with Herr Groos.
The next morning the boys were still at breakfast when the early morning train came creaking into the station, and the first person to come towards the inn was Baron Rosenthal.
He shook Franz warmly by the hand. 'Thanks to you, my boy,' he said, 'the thieves are in prison. It only remains for you to show us where the rest of the silver is hidden.'
The other boys gazed at Franz in surprise, but he was not long in telling the whole story, and explaining how it was that he had been the only boy who had had no time to collect specimens. Half an hour later the whole party started for the Kühberg, with Franz to guide them.