One

"Helga dear," Rowena started, "we were thinking to return back to Hogwarts again! Disguised as students! We wanted to see what it was like again, it was Godric's idea!"

Other Harry Potter Books:

Founders: Back to Hogwarts

Marauders: M O N S T E R

Harry: Pfff.... I'm no Muggle

Albus: Albus Potter and the forgotten muggle