A former acquaintance of Beckett who has turned to a life of crime could be an antagonist. They might have some old grudge against Beckett, like Beckett once reported them for something minor but it led to them having a really hard time, so now they want revenge by holding Beckett hostage.
Another development could be that outside help arrives. Maybe a friend or a law enforcement agency has been tracking them down and manages to stage a rescue at a crucial moment. The story could then focus on how Beckett and Lily reintegrate into their normal lives after such a traumatic experience.
Well, without having read the exact 'beckett and lily held hostage fanfic', generally in this kind of story, the characters would be in a state of high stress. Their relationship might be tested or strengthened during the time they are held hostage. Maybe Beckett is a brave character who tries to protect Lily, or they have to rely on each other's skills to find a way out. The fanfic could also introduce other elements like the motives of the hostage - takers, which could be for ransom, revenge or some other mysterious reasons.
One idea could be that Beckett's friends have to use their unique skills to outwit the kidnappers. For example, if Beckett has a tech - savvy friend, they could hack into the kidnappers' communication system to find out their location. Another idea is that Beckett discovers a hidden strength within themselves during the hostage situation and manages to escape on their own, only to then lead the authorities back to rescue the other hostages.
The plot might start with the Castles family being held hostage in their own castle. The captors could be a group of treasure hunters who believe there is a hidden treasure within the castle walls that the family is hiding. As the family is held captive, they start to discover hidden passages and secrets about their own castle that they can use to their advantage. The fanfic could detail their attempts at survival, their relationships being tested under stress, and finally their escape.
An ancient curse or a malevolent spirit could act as the main antagonist in a more supernatural take on the 'castles family held hostage fanfic'. The family's castle could be built on an ancient burial ground or have some dark history. The spirit holds the family hostage within the castle, and the family has to figure out how to break the curse or exorcise the spirit to free themselves.
Fear is a common element. The hostages are extremely afraid for their lives. Also, there's usually a perpetrator or group of perpetrators with some sort of demand, like money or political concessions.
Using the Son of Heaven to command the vassals referred to a common phenomenon in ancient Chinese political culture. A powerful vassal state kidnapped or threatened the Son of Heaven to obtain the support of other countries and gain more political and economic advantages.
The storyline was usually about a powerful vassal state obtaining the support of other countries by kidnapping or threatening the emperor, and obtaining greater political and economic benefits. However, this behavior also caused dissatisfaction and worry among the other vassal states, which would eventually lead to a fierce political struggle and war.
The story usually depicted a protagonist as the representative of the emperor or the imperial court trying to break free from the control of the princes to maintain the unity and stability of the country. The protagonist might experience various difficulties and challenges, including diplomatic struggles with vassal states, internal political struggles, and wars. In the end, the protagonist successfully broke away from the control of the princes, maintained the unity and stability of the country, and became a hero or legendary figure.
One possible scenario in this fanfic could be that Horatio is desperate to save his niece. He uses all his skills and resources within the CSI Miami team. Maybe Jessoc is somehow involved in the hostage situation, either as an accomplice or as someone who has information that could lead to the niece's rescue. Horatio has to balance his emotions and his professional duties to ensure his niece's safe return.