Well, the fanfic could start with Horatio's niece finding a strange object near their family property. She shows it to Horatio, and he realizes it might be related to an old, unsolved case. They then team up, with Horatio teaching his niece the basics of CSI work as they try to solve the mystery behind the object. Along the way, they face many obstacles, like false leads and people trying to stop them from uncovering the truth.
One possible fanfic could be about Horatio's niece coming to visit him in Miami. She might get involved in one of the cases in an unexpected way, like she witnesses something related to the crime that the CSI team is investigating. This could lead to a series of events where Horatio has to balance protecting her and solving the case.
A third common theme is mystery. Just like in the CSI Miami show itself, the fanfics usually revolve around solving some sort of mystery or crime. The niece might be directly involved in the case, or she could be a side character who is affected by the events. There's also often a bit of drama, whether it's between the niece and other characters on the team, or related to the mystery at hand, like secrets being uncovered that impact the story's progression.
A possible plot is that the OC is a journalist who is covering a big story in Miami. They cross paths with Horatio and Jesse during their investigations. The OC starts to get too close to the truth of a dangerous case and Horatio and Jesse have to decide whether to trust the OC or keep them at bay. As the story unfolds, they all realize they need to work together to expose the real criminals.
One possible fanfic could start with Horatio at the crime lab when he gets a frantic call that his niece has been snatched. He immediately drops everything and starts the investigation. The kidnapper demands a large sum of money in exchange for his niece's safe return. Horatio, using his skills and the resources of the CSI Miami team, starts to track down the kidnapper's location. He follows a series of clues, from the type of vehicle seen at the abduction site to a strange phone call made to a local payphone. As he gets closer to finding the kidnapper, the tension rises and the reader is left on the edge of their seat wondering if he'll be in time to save his niece.
I'm not sure if it's still out there, but there was a fanfic that focused on Horatio's niece joining the CSI Miami team as an intern. It was really cool because it showed her learning the ropes from the more experienced characters. It had some great character development for the niece as an original character (OC), and it also had some nice interactions between her and Horatio, who was being very protective yet also wanting her to grow and learn in the field.
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.
Horatio would be extremely determined. He'd use all his resources and connections. He'd be on high alert and focused solely on getting his niece back. His usually calm demeanor might crack a bit under the stress, but he'd still be in control.
A plot could be that the kidnapper is someone with a grudge against Horatio. Jesse and Horatio's team in CSI Miami follow the leads. Jesse has some knowledge about a similar case in OC. He shares this with the team, and they use it to figure out where the hostage might be held. They eventually find the location and rescue Horatio's niece.
One common theme is the integration of the OC into the CSI Miami team. Usually, the OC has to prove themselves and find their place among the established characters, like Horatio. Another theme is the solving of complex crimes. The OC often brings in a fresh perspective that helps Horatio and the team in their investigations.
Good character development is key. Writers should show how Horatio and Julia grow as individuals and how their relationship evolves. For example, if Julia starts off as a bit of a rookie and Horatio is the experienced one, showing her progress under his guidance can be interesting.