Ron is riding his tricycle and some kids are picking on him. He decides to learn how to ride a two-wheeler, but fails. Meanwhile, Hermione is fighting the Death Eaters. It ends as her getting turned into a bike, and they made it so she can't change back. She tells Ron that he needs to get on her to work the throttle, but he says that he needs training wheels on her first, so he puts them on her.
After Hermione and Ron chase the Death Eaters for a while, the Death Eaters blast off into space. Hermione says that they are going to the planet of the Death Eaters, and Ron has a scary little abstract nightmare, as the planet of the Death Eaters are full of Death Eaters, for a while. When Hermione goes to pick out a space ship to follow the Death Eaters, she initially picks a really high tech battleship, but Ron deems it too scary and makes her take a ladybug ship for old ladies that Professor McGonagall takes for picnics on the Moon.
So they go to the Death Eaters' planet but quickly realize that the planet is full of nice people and pastel colors. They find the Death Eaters and see that they are school administrators. They think that this is a disguise, but then are told that they are really school administrators. But when they get evidence that the Death Eaters are Death Eaters, and the Death Eaters, fearing that their secret will be blown, stupidly get into costume and chase them around, with everyone seeing.
In the end, the Death Eaters' normal lives are utterly ruined, and to prevent evidence of them being all cheery and pastel from getting to their evil friends, they turn Hermione back to normal, and Ron realizes that since the training wheels fell off during the chase, he can now rub it in the bullies smug faces. And he does.