An orthodox Jewish man refuses to accept the marriage of his daughter to a Christian man.

The secret from the title is the lost recipe for shiny Delft pottery, that Jan Vogel is desperately trying to rediscover. For his attempts he needs platinum, but the funds run out because the factory owner Van Haaften has lost his money in stock-speculations. Luckily for Jan, he finds a farewell letter in the park, including a large sum of money. Meanwhile, the owner's son Leo confesses his love for Jan's daughter Annie, but Van Haaften forbids their marriage.

Young poacher Hendrik van Norden has seriously wounded a game-keeper, who has not recognized him. There was, however, one witness: captain Van Oort, but he promises to keep silent. Five years later Hendrik has become a lighthouse-keeper and is courting Annie. Van Oort is also trying to win Annie's affections, and in his jealousy he decides to remind Hendrik of what he knows about his past...

When his granddaughter is born, debt-ridden Colonel von Zwenken misses out on Aunt Roselaar's allowance of 20,000 guilders. Anxious to keep the money, his son-in-law telegraphs the aunt that a son was born, Frans, and the girl is brought up as a boy. Based on the novel by Anna L.G. Bosboom-Toussaint.

A collection of short scenes portraying highlights of Dutch history, from the Eighty Years' War to King Willem I's return from exile. This film was made to commemorate the centenary of the Dutch royal family.