After the death of their father, a travelling showman, Iris Belmore and her little brother Billy are engaged to play in a circus owned by George Munro. Jim, a young man their father had adopted, comes home after he has been at the sea, where he has saved the lives of Lady Rosemount and her son during a shipwreck. Jim, a sharpshooter, also joins Munro’s circus and shows Iris and Billy much kindness. Iris and Jim do a sharpshooting act together. Munro’s jealousy is aroused when he sees that their friendship is growing into love. In revenge he tampers with Jim’s revolver, with the result that an accident happens in the ring and Iris is slightly wounded. Jim gives Munro a severe thrashing and leaves the circus, taking Iris and Billy with him, in search of other employment. While tramping the country, they meet Lady Rosemount and her husband. Sir Henry, hearing their story and wishing to show his gratitude, buys Munro’s circus and makes Jim the manager, on condition that he marries Iris. ×

Lona, a young woman who has no memories of her past, has been adopted by the rich industrialist Van Haaften. She is loved by Henri van Rhenen, a neighbour whose mother still mourns the loss of her daughter, who disappeared twenty years ago under mysterious circumstances. Lona has another suitor, Frans van Borselen, who hopes to marry her so that he can pay his gambling debts with her foster-father's money. Van Haaften discovers that Frans has been cheating at cards and offers him a revolver so that he can end his life honourably.

Dolores gets a marriage proposal from the promising young doctor Lucas, but on the day of their marriage, she leaves him in the lurch and takes off with the South American dancer and adventurer Hugo Amadis. But Hugo treats her badly. Dolores leaves Hugo and begins a career as a dancer to make ends meet for her and her son. One day, the son gets sick, and the doctor who helps the child through the crisis is Doctor Lucas. Lucas and Delores decide to start over.

The wealthy Alice Stanton is saved from drowning by Jack, a fisherman who sees her in the water. They get to know each other and begin a romantic relationship. This comes to an end when Jack realizes that the people will never approve of their relationship. He fears that their difference in social status will cause a scandal. He ends their relationship and breaks off contact. Six months later, Annie marries someone else. Meanwhile, Jack spends all his time at sea and is involved in a shipwreck. He is seriously injured and, just before he dies, he has a vision of Alice.

A cabinetmaker finds a document written in Latin in an old desk. Because he cannot decipher it, he asks his lawyer for a translation.

Kate van Marlen is blissfully happy with her partner, Count Alfred van der Loo. However, he has no serious plans for her and says he will never marry her. The young, spirited cavalry lieutenant Count Ruprecht van Halden thinks differently: for him, Lady Kate is the ideal woman. He courts the young girl and asks for her hand in marriage. Kate makes one last attempt to win Alfred over. During a garden party, she confesses her love to him once again, but Alfred refuses.

On the verge of getting married to Marijke, young and insecure detective Jozef is assigned the case of a murdered factory girl. His relationship is threatened when he becomes madly infatuated with Carmen, the alluring prime suspect.

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.

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.

A poor fisherman's wife sends the remaining family members, her two sons, out to sea on a boat that has seen better days.