The guests at Count Otto von Trepow's East Prussian estate Gross-Ehrenfeld are Lord and Lady Ruthven, Mr Hendriks with his wife and foster-daughter Mariska, a gypsy they adopted years ago, Kundry, the fiancée of Otto's son Bernhard, and Count Stanislaus Larinski, who claims to be a Polish revolutionary wanted by the Russian government. A boating trip is organized but ends when the motor breaks down. While waiting for it to be repaired, the guests go to an inn run by Andreas and his daughter Käthe. Hendriks goes for a walk, sees the boat come back and that a man with a bent back leaves it. He notices that Kundry is afraid of Bernhard.
Ducrot and Ninette accuse Mario and Anny of owing their wealth to the murderous effects of Mario's bombs. Anny leaves for the front to care for the wounded. Third part of Maurits Binger's epic silent trilogy. Most of the film is considered lost – a single fragment remains.
Anny helps Mario escape from prison after his attempted murder of Gaston de Roqueville, who is now married to Ninette. Banker Sorga, an enemy spy, attempts to steal Mario's latest invention: a powerful explosive that could alter the course of the war. Second part of Maurits Binger's epic trilogy, now considered lost.
In the prologue, a boat with some shipwrecked persons is drifting at sea. Among them is Baron van Waldheim, who, before he dies of exhaustion, entrusts his little son Alfred to the care of his butler Hendrik. The evil Jan van Oort persuades Hendrik to give him the Baron's papers. When they put the boy ashore, he wounds himself on a nail (leaving a scar that will later prove his identity). For years Van Oort manages to pass himself off as Baron van Waldheim; he is married and has a daughter and a son. One day Hendrik turns up demanding a job as butler, swearing that otherwise he will betray Van Oort's secret. Meanwhile, Alfred - now an adult known as Ulbo Garvema - has become a teacher. Unaware of who Van Oort really is, he accepts the position of tutor to Van Oort's children. He falls in love with the daughter, but Van Oort refuses to give his consent to their marriage. Ulbo and the girl elope.
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.
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.