Rosario, Cesare and Cesare's brother Antonio were once three friends who came from the same village in Sicily. In their youth, all three saved enough money and decided to go off to seek new opportunities in the United States. Cesare and Antonio decided to turn to a life of crime and joined a criminal gang. Rosario prefered the straight path and subsequently became one of the richest men in the country. When Antonio and Cesare were arrested for the murder of a policeman, they appealed to Rosario for help but he refused to have anything to do with them. Antonio was executed and Cesare jailed for ten years. Cesare blamed Rosario for his death, and swore to take revenge.
To make things worse, a girl from their home village who have been betrothed to Cesare came to the United States looking for him. Unable to find Cesare or his brother, she looked up Rosario. Rosario had to explain what happened to the two brothers and gave her some money support herself. Some months later, Rosario married the girl himself. When Cesare heard of this, he swore a blood oath to get even with the two of them.
Rosario's wife died shortly after giving birth to their son Carlo thus sparing her from Cesare's wrath. However, Rosario knew that either he or his son who soon become Cesare's target when he was released from prison. Rosario took every precaution, thus effectively locking his son up in a gilded cage. This did not, however, save his son--he was kidnapped while fishing on a lake in his private estate. Although the boy had been heavily guarded, they forgot the third dimension: the kidnapper had landed in an amphibian. Carlo, who was probably chafing under his restricted life style and who had an avid interest in aviation and fishing, climbed on board willingly and was subsequently taken by Cesare to Scotland on a supposed fishing holiday, all along, not even thinking that he had been kidnapped.
Rosario offered a million dollars for the return of his son, or a hundred thousand for any information about his son but nothing was forthcoming. Cesare was not motivated by ransom--he was pursuing a blood feud and his purpose was to torment Rosario by separating him from Carlo.
Be that as it may, Cesare probably had a change of mind as Rosario subsequently travelled to London, on urgent business, so it was claimed. It was believed that Cesare must have contacted him and arranged to meet and negotiate. The Viper, one of Cesare's criminal enemies also learnt about Rosario's trip (probably through press reports about Rosario's movements). The Viper called on Rosario at his hotel and offered to retrieve his son for him. When Rosario declined, the Viper pulled a gun and demanded detailed of his meeting with Cesare. Having got them, the Viper departed in pursuit of his enemy.
Towards the end of the book, when Biggles and his friends had rescued Carlo, Rosario flew up to Scotland to meet his son and thank his rescuers. He was almost overcome by joy in the reunion but told Biggles sadly that he had the misfortune to be a rich man. All his money had ever brought him was anxiety and grief.