Dumbledore's Army
One night, Harry has a vision of Voldemort's snake Nagini seriously injuring Arthur Weasley. Harry tells Professor McGonagall and Dumbledore, and Arthur is rescued. Dumbledore arranges for Harry to take Occlumency lessons with Professor Snape, another member of the Order, to protect his mind against invasions by Voldemort. Umbridge is eventually given a tip-off about Dumbledore's Army, and to prevent Harry's expulsion, Dumbledore takes responsibility for the group, and goes into hiding. Umbridge becomes headmistress.