At Hogwarts they decided to have an exchange program among the houses. One member of each house is sent to spend the year with another house and of course, Hermione is chosen to room with the Slytherins.
The trio are invited back to Hogwarts to finish the education they missed out in their seventh year (original concept - I know). However, McGonagall requests that they stay in the Slytherin dorms due to a bullying incident. Oh my god they have to share a dorm with Draco, who coulda guessed it. Anyhoo, I'm a sucker for Drarry, so the plot's pretty easy to guess. Hope you enjoy, leave a vote etc, etc...