One possible plot could be that Rabastian has some dark motives related to Hermione's magic abilities. Maybe he wants to use her knowledge of spells and potions for his own evil schemes. He could hold her in a secret location, and Hermione would have to use her wits to try and escape or send out some sort of magical signal for help.
Well, perhaps Rabastian kidnaps Hermione as a way to bargain with the Order of the Phoenix or Hogwarts. He might think that her value to those groups is so high that they would be willing to give him something precious in return, like a powerful magical artifact or certain information. Hermione, in the meantime, would be trying to figure out his weaknesses while being held captive.
Dumbledore could play a crucial role in her rescue. He has great wisdom and powerful magic. He might sense that Hermione is in danger through his magical connections. Then he could send some of the more skilled members of the Order of the Phoenix, like Sirius or Lupin, to find and rescue her. They would be able to use their combat skills and magic to overpower Rabastian.
One possible plot could be that the other characters, like Harry and Ron, immediately start a rescue mission. They might search for clues about where Dolohov has taken Hermione. Maybe they discover that Dolohov is working for a more powerful dark wizard who wants Hermione for her knowledge of magic. Then they have to face various traps and dark spells to reach her.
A common plot twist is that Hermione actually has a hidden power or ability that she reveals during her captivity. For example, she might be able to use a type of magic that Draco and his associates didn't expect, which gives her an upper hand in the situation. This could lead to a change in their relationship dynamic, from captor - captive to something more like equals.
In this type of fanfiction, it might be that Harry has been misled by false prophecies. He kidnaps Hermione thinking he is doing the right thing. As the story unfolds, Hermione uses her intelligence to make Harry see the truth. They then team up to face the real threat that was behind the false prophecies all along. It could also involve a lot of emotional turmoil between the two characters as they deal with the situation, with their friendship being put to the test.
One possible plot twist could be that Hermione uses her intelligence to outwit Dolohov even while kidnapped. Maybe she manages to leave hidden clues for her friends to find her. Another could be that Dolohov has an ulterior motive other than harming her, like using her as a bargaining chip in the wizarding war. Or perhaps Hermione discovers a hidden power within herself during the time of her captivity that helps her escape.
One possibility is that it could be a dark and twisted take on the relationship between Draco and Hermione. Maybe in this fanfiction, Draco has some ulterior motives that lead him to this extreme act. It could explore themes of power and control as he forces Hermione into a situation she doesn't want. However, it also might lead to a redemption arc for Draco as Hermione tries to change his ways.
In most of these fanfictions, Hermione reacts with her characteristic intelligence. For example, in 'The Captive Hermione by Greyback', she immediately starts to analyze her surroundings and look for possible escape routes. She uses her knowledge of spells and potions to try and gain an advantage over Greyback.
Hermione would likely react with her usual intelligence and quick - thinking. She might start by trying to analyze Dolohov's motives and weaknesses. She could also try to find a way to communicate with the outside world, perhaps using magic in a very discreet way.
Hermione would likely be defiant at first. She is a brave and strong - willed character. So, she would probably try to resist Narcissa's attempts to intimidate her and would look for ways to escape immediately.
Obviously, Harry Potter could be the one to save her. He has a strong bond with Hermione and is very brave. He'd stop at nothing to rescue his friend. He might use some of his unique magical abilities, like his connection to Voldemort, to find her.