When they got to school they had a feast like last year. Then went back to their rooms. That Halloween they were at a party for Nearly Headless Nick a ghost at Hogwarts School for Witchcraft and Wizardry.
When Harry Heard a voice Harry went to investigate. Ron and Hermione couldn't hear the voice. Then they start to find more and more victims petrified around the school. Everyone suspected Harry of it.
But it turned out to be a boy from Hogwarts named Tom Riddle (Lord Voldemort) only an image out of a diary that Jenny, Ron's younger sister, who was being controlled by it! When they found Jenny she was in an awful state knocked unconscious on the floor. She nearly died but luckily she survived.