Finding Animagus

Before James, Sirius, and Peter can become illegal Animagi they must first learn how to. But what happens when McGonagall steals the book they are learning from. They have to either sneak in her classroom and find it. Or give up. And giving up isn't the Marauder style. Written for Fortnightly Challenges Thread Build a Monster Workshop on Hogwarts School of Witchcraft and Wizardry.