Not a Vanishing Cabinet
(Disclaimer: I don't own Doctor Who or Harry Potter.)
Draco stood in the entrance of the room of requirement. He was staring at a large blue box that definitely hadn't been there the day before. On it were the words 'Police Box'. It wasn't a vanishing cabinet. Or if it was it was one of the strangest he'd ever seen. But if it was as muggle as it looked, he couldn't imagine why it was being hidden here.
Draco stepped forward. There were instructions on the box that said 'pull to open'. Opening it would help identify what is was, so he grabbed the door knob to do that, but then it opened from the inside.
A man stood staring at him for a moment before smiling and saying, "Hello. I'm the Doctor."
