You were 9 years old, a first year, because you had skipped a few years of elementary, always excelling in your classes. But the Weasley twins, thought it would be funny to lock you in a hall closet as a prank.

they were going to come back and get you, but forgot, as they were too busy with the fireworks they were setting off to prank Umbridge in the study hall.

While the fireworks were fun for everyone else, the sparks filled the open vent, that led into the closest you were locked in, and sparked a little fire, that got bigger, and began to burn you