My friend, with the time machine! Well, he's sort of my tutor, too, actually! See, because the headmaster of my school got killed and the people who took it over wouldn't let magical kids with non-magical parents come back, which is me, but then I met the Doctor and he offered to let me travel with him sometimes for educational reasons! He's not a wizard, though, he's just very, very, very, very smart! Like, ridiculously smart!