Severus Snape Confronts the Group with Evidence from the Marauder's Map

Severus Snape reveals himself after finding Harry's Invisibility Cloak near the Whomping Willow and discovering evidence on the Marauder's Map. He accuses Remus Lupin of helping Sirius Black enter the castle and aims to take both Lupin and Black to Azkaban, believing this will prove his longstanding suspicions about Lupin's loyalty. Lupin tries to explain, but Snape, consumed by his schoolboy grudge, ignores him and binds Lupin with magic.