McGonagall was a Death Eater spy. Hey, if Snape can play the long con, why can’t another character?
What a load of waffle! But….
- She stakes out the Dursley’s house as an animagi cat, and Dumbledore is surprised to see her there.
- Unlike all other teachers at Hogwarts, including Snape, she teaches Harry nothing he can use later against Voldemort.
- During Harry’s first Quidditch match, he rides a jinxed broom that she gave him.
- More here.