This is a historical novel and the story begins with the 1672 lynching of the Dutch Grand Pensionary (roughly equivalent to a modern Prime Minister) Johan de Witt and his brother Cornelius by a wild mob of their own countrymen. The main plot line, involving fictional characters, takes place in the following 18 months.
Cornelius Van Baerle of Haarlem is a lover of tulips and he has succeeded in producing the bulbs of black tulip for a competition which offers a prize of 100,000 guilders. The murdered Cornelius de Witt was his godfather and he was arrested on behalf of this connection and also bcoz of some letters. This prevented him from planting the bulbs and it was given secretly to Rosa, the beautiful daughter of the prison-keeper.
The first bulb got crushed by her father, but she brings up the second one carefully. Isaac Boxtel, Baerle's neighbour, steals it and Rosa gives a complaint to the President of the Flower-growers. Prince of Holland helps her, the truth is found out and the prize is given to Rosa. Baerle is proven innocent and he marries Rosa.
Book was originally published in three volumes in 1850 as La Tulipe Noire and as I hv read a simplified version (which is really small), there is nothing much to add. This version gives no stress to the historical background and my impression was that of a children's story at that time. So go for the original, you can download it from internet.