Jan Vogel works in the Van Haaften china factory; he wants to uncover the secret of the splendour of Delft blue china. And he succeeds, but when Van Haaften commits suicide, he is suspected of murder and arrested. Willem Berg, diabolical nephew of Jan Vogel takes his place in the factory and declares that he knows the secret. In reality however he is not at all aware of it and attempts to get Vogel to reveal it to him. But Vogel’s daughters discover Berg’s plans, manage to keep the secret out of his hands and prove their father’s innocence.

A nitrate print of the film was found in 1994 in a private collection by the staff of the Film & Science Foundation and was entrusted to the Nederlands Filmmuseum for its restoration. Up till that moment Het Geheim van Delft was one of the many lost Dutch silent films. In the 1910s, the Hollandia Filmfabriek became the most important Dutch studio for the production of fiction films and Annie Bos was the main star of the period. Note are the acrobatics in the last part of the film (up until a short time ago known to us only through written sources) – they were performed by Annie Bos herself.