Oh! This story is in the BEST tradition of Redeemed!Dudley! And pairing him with Millicent is brilliant. I love how you wrote her as just a little awkward and bookish, yet willing and able to clobber a fellow student who is torturing a younger student.
The riffs off Modesty Blaise are brilliant as well--as are the riffs on Doctor Who!
The meeting at the safe house! The right-raising of Harry!
It's a brilliant universe, and one I'd love to see more of.