Returning from Greece, where he has lived for some years, Jan Stephorst - travelling incognito as 'Captain Zeppos' - has taken up residence at the Molenhoeve (the mill cottage). All the villagers in Belder, except young Ben Kurrel, distrust this mysterious man.

Captain Zeppos tells Ben in confidence that he is one of the heirs of the Belderbos castle and estate. When he stayed in Greece a stranger he calls 'The Mole' (a nickname inspired by the mole on his face) offered him a considerable amount of money for his inheritance.

The Mole, together with another person wearing a black leather jacket are seen around the Belderbos estate. Ben Kurrel and Rita Mees, the baker's daughter, warn Captain Zeppos but when he arrives at the mill cottage, he discovers that there has been a break-in.

Rita sees the stranger in the black leather jacket with an old music box. The tune from the box seems familiar to Captain Zeppos, but he can't remember why straight away. Suddenly, he realises that it must be the music box that once belonged to his uncle Nico.

Episode 5: De Geheimzinnige Kamer
(Translation: The Mysterious Room)
Wednesday 18th November 1964, 5.00-5.25pm

Captain Zeppos and Ben Kurrel set off to investigation the castle on the Belderbos estate. In their searches, they discover a hidden room. It transpires that this once was the room of Aunt Irene, a woman who had died at a tragically young age and who had been the wife of Nico Stephorst.

Zeppos and Ben come to the conclusion that the mysterious young woman in the leather jacket is Ariane Despinal, niece of Nico Stephorst and second heir to the Belderbos estate. Their continued investigations begin to bear fruit, as they locate the hideout of The Mole and Ariane.

Episode 7: Het Testament
(Translation: The Will)
Wednesday 2nd December 1964, 5.00-5.25pm

The Mole holds Zeppos and Ben prisoner but they are able to make their escape. An old servant from the castle, Maaike, informs Zeppos about the existence of a will, the contents of which are to his advantage. Meanwhile, Rita finds a new clue to the mystery of the will's whereabouts.

Ben and Gust keep watch while Zeppos confronts Baral, the leader of the gang. Baral urges Zeppos to sell his inheritance. Zeppos refuses and receives a warning: a square nail.

Kapitein Zeppos has disappeared without a trace and Ben fears the worst. Acting on instructions left by his friend, Ben visits the Captain's solicitor. Ariane is surprised and claims to have no involvement in the crime.

The drilling site on the Belderbos estate is prepared, with Post, an American drillmaster, leading the operations. Ben witnesses a major dispute between Ariane and Baral's gang about the attack on Kapitein Zeppos. He tries to investigate, but receives a warning from Baral's gang.

Ben receives a great surprise. Zeppos is alive and well. Ariane and Zeppos, the quarrel between them settled, go into hiding in the city to escape Baral's gang. In spite of the danger, Ariane decides to go for a walk. She is noticed by one of the gang members.

Ben and Zeppos leave their hiding place to search for Ariane, only to discover that Baral is already on her trail. Baral wants her dead, at any cost. At the house, Ben and Zeppos notice a guard. They overpower him and discover a message there for the Captain.

Trying to find Ariane, Zeppos and Ben follow two men who are acting suspiciously, but they have walked into a trap. Inspector Peters frees them and the three men join together to search for the gang's headquarters.

Baral makes a proposition to Ariane, while Zeppos is lured to the mill cottage with a false emergency phone call. Rita and Inspector Peters rush to the mill, but when they arrive, they find Ben but no sign of Zeppos. At the drilling site, work is ready to commence.

Baral has both Zeppos and Ariane in his clutches as he makes preparations to blow up the quarry - and them with it. The signal for evacuation is given, but Inspector Peters, Ben, Rita and the police are on their way. The police surround the quarry and this leads to a final confrontation with Baral and his gang.