One possible plot could be that Dumbledore has been possessed by a dark entity. Under its influence, he kidnaps Hermione thinking she has some knowledge or power that the entity wants. Hermione then has to use her wits to try and break Dumbledore free from the possession while also trying to escape.
A possible plot could be that Dumbledore has made a deal with a dark wizard in the past. As part of the deal, he has to deliver Hermione. He kidnaps her but then has second thoughts. Hermione, being the intelligent witch she is, tries to convince Dumbledore to break the deal and turn against the dark wizard. Along the way, they face many challenges and Hermione has to deal with the fact that her once - trusted mentor has betrayed her.
There could be. Fanfiction writers love to explore different scenarios that deviate from the original story. But it's important to note that this goes against the general perception of Dumbledore's character. In the official Harry Potter series, Dumbledore is a protector, not a kidnapper. But in the world of fanfiction, anything is possible.
Well, perhaps Dumbledore has some dark secret and believes Harry is the key to it. He might kidnap Harry to keep him away from Voldemort in a very unorthodox way. Maybe he wants to train Harry in isolation for some super - powerful magic that he doesn't want Voldemort to find out about.
Perhaps Bellatrix kidnapped Hermione to use her as bait to lure Harry. Bellatrix has always been extremely loyal to Voldemort and might think that by having Hermione, she can draw Harry out into the open. Hermione, being the intelligent witch she is, could try to outwit Bellatrix while in captivity, maybe by finding a way to send messages to her friends or even by trying to escape on her own.
The plot could take a turn where Zabini is initially seen as the bad guy because of the kidnapping, but in reality, he is trying to protect Hermione from a greater threat. Maybe there's a prophecy that involves Hermione and Zabini, and the kidnappers are trying to stop the prophecy from coming true. Another possible twist is that Hermione's kidnapping leads to a discovery of a long - lost magic that Zabini's family has been searching for. This magic could change the balance of power in the wizarding world, and now Hermione is in the middle of it all.
In a more extreme case in the fanfiction, Dumbledore might assign Hermione to a special project that is both difficult and dangerous as a form of punishment. For example, he could send her to study a group of cursed magical creatures in the Forbidden Forest. This would be a punishment that not only tests her skills but also her courage.
It could also be that Dumbledore has some secrets that he's afraid Hermione will uncover if she's left to her own devices. Hermione is known for her inquisitive nature. So, to keep these secrets hidden, he attempts to control her. For instance, if there are some hidden aspects of Hogwarts' history or certain faculty members that he doesn't want exposed, he might use control over Hermione to prevent her from delving too deep.
Perhaps in this fanfiction, Dumbledore has a secret plan related to Harry's power. He might think that by kidnapping Harry, he can train him in isolation to fully develop his magical abilities without the distractions and potential dangers at Hogwarts. It could also be that Dumbledore is trying to hide Harry from Voldemort in a way that no one would suspect, as Voldemort would never think Dumbledore would use such extreme measures against Harry.
In one possible plot, Voldemort might kidnap Hermione to use her knowledge of magic against Harry. He could try to force her to reveal secrets about Dumbledore's plans or the location of certain powerful magical artifacts. Hermione, being strong - willed, would resist and try to outwit Voldemort using her intelligence.
One possible plot could be that Hermione discovers a hidden family secret that reveals she is Dumbledore's sister. This leads to her having access to new knowledge and powers that Dumbledore left for her, which she uses to fight a new dark force in the wizarding world.
One possible motive could be Bellatrix's loyalty to Voldemort. She might think that by kidnapping Hermione, she can get information about Harry Potter and the Order of the Phoenix. Hermione is known to be very intelligent and Bellatrix could believe she has valuable knowledge. For example, Hermione might know the location of Potter or the Order's plans against Voldemort.