Starting with the author, Alex Michaelides studied screenwriting and wrote the successful "Silent Patient". He's known for psychological thrillers with unreliable narrators. The sequel is likely to continue exploring Theo's trauma and perhaps his struggle with the truth.
Themes could include identity, truth vs. perception, psychological trauma, justice. Character development would focus on Theo's mental state, his coping mechanisms, and maybe a new character involved in the crime. La furia - Alex Michaelides -2-.epub
Also, check if there's any official information from the author about the sequel. From what I recall, Michaelides mentioned on social media about "The Fury" being a sequel where Theo is falsely accused of a new crime. If I can reference that, it would be better. For example, maybe a new case where Theo is the suspect in a murder that he didn't commit, forcing him to uncover the truth while dealing with his guilt from the past. Themes could include identity, truth vs