There was a boiler room in the school attended by C. S.. At some point, there was an explosion in the boiler room, and when C. S. got separated from their classmates upon attempting to leave the school, they found themself outside the door to the boiler room. The Ninth Doctor exited it, told C. S. they needed a new boiler, and left in the TARDIS. (PROSE: Have You Seen This Man?)