It's Christmas at Hogwarts and Harry, Ron, and Hermione are ready to unleash their Polyjuice Potion plan.
Harry and Ron just need some hair from Crabbe and Goyle's head. Hermione's got this one figured out, too.
Ron and Harry float some cupcakes in the hall and Crabbe and Goyle grab them and chow down. Of course, Hermione's laced the treats with a sleeping draught so they pass out. Those guys are thick.
Back in the girls' bathroom they add the hair to their potions (Hermione's swiped some from some from Millicent Bulstrode's robes). They drink and start to transform.
Harry successfully turns into Goyle and Ron is Crabbe, but Hermione won't come out of the bathroom stall. She tells the boys to go ahead without her. They only have an hour before the change back into themselves.