9 down: (4,5) BEAR/CROSS
17 ac (6) SADIST
45 d (6) AROUSE
41 d (6) OLEONE
and finally;
53 ac (5,4) BALTI/LOAF
Obviously, in the absence of any actual clues, these can only be wild guesses. If you'd care to supply the aforementioned clues, you might get some more sensible suggestions.
Think you've cracked the theme (which was driving me crazy!!) 52a Doctor who (Matt smith is the 11th doctor!!) Off to find things with 20 and 11 now - thanks!!!