Dr Kroch, healer of all ailments, wounds, bites and fractures, receives a heavy coffer. His assistant Valet lifts the lid and utters a cry of surprise, but the doctor, wholly unimpressed, stirs the contents with his foot. All this, however, is observed through the window by a robber's greedy eyes. It is not long before the doctor is visited by a strange patient, who reawakens his interest in the coffer's contents.
On their way to Wolf Castle, Dr Kroch and his assistant Valet stop at a monastery. The monks worship someone named Willibald, who apparently performs miracles. Indeed, strange things happen... as robbers Oenk and Boenk, still pursuing the doctor's gold, find at their expense.
On their way to Wolf Castle, Dr Kroch and Valet are confronted with a lovely patient, who is haunted by visions of Wolf Castle. It has something to do with a ring, and is therefore very contagious. Even robber Boenk is affected.
Does Wolf Castle only exist in dreams? Sylvia's gold ring, which conjures up visions of it, has unfortunately been lost. Dr Kroch and Valet accompany Sylvia home, but the people at the inn appear to know more about the castle. Especially the mysterious gypsy fortune-teller, who asks the doctor to dance with her.
Sylvia has disappeared without a trace, and Wolf Castle turns out to be in ruins. The Duke has been dead for centuries. To Valet, further investigation is pointless; he wants to go and search for Sylvia. At the fair, a pageant play of an old legend puts the case in a different light, to the doctor and his assistant as well as to robbers Oenk and Boenk.
Is there any truth to the pageant play? Dr Kroch wants to get to the bottom of the matter. Valet wants to find Sylvia, and the stolen gold as well. All tracks lead to the ruins, only to come to a dead end. Until night falls and the howling of a wolf heralds the revival of a vision.
Has Dr Kroch finally found the Duke of Wolf Castle? How can ruins suddenly transform back into a castle? The learned fellow racks his brains over it. Valet has problems of his own, which he struggles to solve. Oenk and Boek seem to have found a robbers' paradise, which appears to be anything but paradisaical.
The nocturnal festivities of Wolf Castle have ended abruptly and painfully for the "dowager", but Sylvia has returned, to Valet's great pleasure. Wolf Castle appears to be no dream, but then what is it? The gypsy woman is convinced it is magic, and the robbers' experiences with the gold at Wolf Castle seem to suggest she might be right.
Just as the gypsy woman foretold, Dr Kroch has disappeared. Has he been lured to Wolf Castle, or did he go of his own free will? Every night, the castle rises from its ruins, full of live inhabitants; it is said that a golden city, the Duke's residence, is located underground. Sylvia and Valet decide to venture there to find the doctor, for the Duke is said to be a dangerous man with magical powers, as Oenk and Boenk have discovered to their cost.
Sylvia and Valet narrowly escaped the phantom robber barons' wrath by stopping the time clock. The entire castle is magically frozen. Together, they descend the spiral staircase. In the meantime, Dr Kroch has reached the Duke of Wolf castle, the patient suffering from gold fever. It appears to be a curious disease.
Dr Kroch has some strange adventures with the Duke of Wolf Castle. Things get curiouser and curiouser. The learned fellow is thoroughly confused by the inexplicable and unbelievable phenomena he witnesses. The two robbers keep finding more gold they cannot touch. Sylvia bravely soldiers on, and Valet suddenly discovers he has a great power.
Valet has dispelled the wolf with his "evil" eye. The Duke is cured of his gold fever, and Sylvia accompanies Valet to the phantom castle to fetch the Duke's brothers. Dr Kroch remains in the golden city, where the two robbers are still trying to make a killing, and the wolf is still on the loose.
Dr Kroch has proved to be stronger than the wolf. He uses its power to undo all the magic. At the spectral castle, time passes relentlessly, calling into question the possibility of a safe return from the underground city. The gypsy woman's unexpected arrival could be crucial to the outcome of this adventure.