The Day That Killed Blaise Zabini

When Draco Malfoy has an argument with his fellow Slytherin, Blaise Zabini, Blaise casts a spell that causes Draco's consciousness to switch with the Head Girl's, leaving him stuck inside her body, and she, stuck inside his. Now they've got to find a way to reverse the spell and switch back, but only Blaise Zabini knows the counter curse. What's more: Hermione Granger is the Head.