Snape Teaches Neville to be a Spy
Set while Snape is headmaster during DH: - Neville leads the student rebellion against Headmaster Snape. But what no one knows is that Snape himself recruited Neville for this role, the rebellion is a diversionary tactic, and Neville and Snape are working together for a mysterious goal. And Yay! if you make it slashy!