Thanks, however, to the vigilance of Colonel von Rochow, his keeper, and to the panic of his page, Frederick did not even mount the horse that was to have borne him out of Germany. His abortive attempt inaugurated one of the strangest tragedies in history. From the very fact that he was the guest of other princes Frederick William could not act in haste. The scheme was betrayed to him at Mannheim on August 6th, and he ordered von Rochow to deliver his son to him at his own town of Wesel, alive or dead. In this mood they continued the tour of pleasure, sailing down the Rhine and visiting the potentates upon its shores. At last, on the evening of the 12th, they reached Wesel. Frederick William at once interrogated his son, who lied and protested his submission. The King replied by despatching him to Spandau under the care of a general, who was enjoined to frustrate any attempt at rescue by killing his prisoner.
Spandau is the fortress near Berlin where to-day the Prussian sentries guard some millions of the treasure wrung from France. It was not deemed safe enough to keep the Prince of Prussia. “He is very cunning,” wrote the King, “and will have a hundred inventions for making his escape.” A stronger gaol was sought for. In a sombre plain east of the capital lies Cüstrin, whose grim fortress marks the spot where the sluggish Wartha gliding down from Poland silently joins the Oder. There, on September 4th, Frederick was imprisoned. On the way he had faced a tribunal of soldiers and lawyers with a jaunty confidence which showed that though he might cower before the King he had not forgotten that he was still Crown Prince of Prussia. It was rumoured that he had poked fun at Grumbkow, his father’s most trusted counsellor. For himself he asked no favours, but avowed his responsibility for all that Katte had done amiss.
A fortnight later, on September 16th, the commission examined him again. In the meantime he had begun to understand the nature of a gaol. His father, who lived in such a state of frenzy that he ordered that the tongue which spoke of this affair should be cut out, had not scrupled to condemn him to solitary confinement, a penalty often destructive of health and not seldom of reason. He was clad in brown prison dress, fed on the humblest fare, and deprived of light at seven o’clock in the evening. Thus prepared, he was subjected to a merciless inquisition. After more than one hundred and eighty questions of fact, came two which the King had commanded the interrogators to add. “Do you wish that your life should be granted to you or not?” “I submit to the King’s mercy,” answered Frederick, adding in pencil, when the report was laid before him, “and to his will.” “Since by violating your honour,” ran the last question of all, “you have made yourself incapable of succeeding to the throne, will you renounce the succession by an abdication that shall be confirmed by the whole Roman Empire—to save your life?” “My life is not over-dear to me,” replied the Prince, “but Your Majesty would surely not be so ungracious to me”—and he added a prayer for pardon. The King tore up the petition and applied his genius for detail to a code of rules for the torment of his heir. No one was to speak to the prisoner. Three times a day the door of his room might be opened, but within four minutes it must be made fast again. Mute attendants were to set before Frederick food which they had cut in pieces, since the royal command deprived him of knife and fork. For Katte Frederick William had ordered the rack, but on the representations of Grumbkow the order was cancelled. For his son he discovered a torture which Grumbkow himself was to apply. “He must be told,” decreed the King, “that no one thinks of him any more; that my wife will not hear his name; that his sister Wilhelmina has fallen under my displeasure, that she is shut up in Berlin, and will very soon be sent into the country.”