While we're still on the topic of Harry Potter... let's riff on Jeconais' "White Knight, Grey Queen" and any number of other fics with the same initial device:
Harry is rescued from some seriously bad situation at the Dursleys by a Slytherin girl and her family, who nurse him back to health while proving to him their desire to be neutral or their secret goodness or some such. They encourage Harry to form a third side with evidence that Dumbledore is at the very least senile and at worst actively manipulating Harry. They heal him, train him, and help him -- and he decides that before he can take out Voldemort, he has to take out Dumbledore first, or else Dumbles will either a) foul everything up, b) stab him in the back and deliver him as a "sacrifice" to the prophecy, or c) stab him in the back after he's won and take credit for it. However, the moment he defeats Dumbledore, Slytherin girl and her family do the back-stabbing, and Voldemort rolls over Wizarding Britain like a snakefaced blitzkrieg. For extra angst, Slytherin girl reveals that she really and truly does luuuuuuuve Harry, and tells him no Slytherin boy can measure up to him, but the family's allegiance to Voldie is more important than her happiness -- family honor and all. She'll always treasure the time she had with him, and she probably will never be happy with any other man... but she has to kill him now, sorry.
-- Bob
---------
Then the horns kicked in...
...and my shoes began to squeak.
Harry is rescued from some seriously bad situation at the Dursleys by a Slytherin girl and her family, who nurse him back to health while proving to him their desire to be neutral or their secret goodness or some such. They encourage Harry to form a third side with evidence that Dumbledore is at the very least senile and at worst actively manipulating Harry. They heal him, train him, and help him -- and he decides that before he can take out Voldemort, he has to take out Dumbledore first, or else Dumbles will either a) foul everything up, b) stab him in the back and deliver him as a "sacrifice" to the prophecy, or c) stab him in the back after he's won and take credit for it. However, the moment he defeats Dumbledore, Slytherin girl and her family do the back-stabbing, and Voldemort rolls over Wizarding Britain like a snakefaced blitzkrieg. For extra angst, Slytherin girl reveals that she really and truly does luuuuuuuve Harry, and tells him no Slytherin boy can measure up to him, but the family's allegiance to Voldie is more important than her happiness -- family honor and all. She'll always treasure the time she had with him, and she probably will never be happy with any other man... but she has to kill him now, sorry.
-- Bob
---------
Then the horns kicked in...
...and my shoes began to squeak.