"...once we've drunk it, we'll have exactly an hour before we change back to ourselves."
-- Hermione Granger (CS12)
Crabbe and Goyle are drugged (by some Sleeping Draught that Hermione puts in some chocolate cakes) and have their hair stolen by Harry and Ron. They add their hairs to the potion and drink it in the bathroom.
Disguised as Crabbe and Goyle, Ron and Harry quiz Draco Malfoy and find he has nothing to do with the Chamber of Secrets. Upon returning to the girls’ bathroom they find Hermione has taken on cat features.