Verne's captain (4)
I believe the answer is:
'verne's captain' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for nemo that I've seen before include "Jules Verne's submarine captain" , "Captain brought to book" , "Jules Verne captain" , "- me impune lacessit (motto of Scotland)" , "Finding -, animated film" .)