King imprisons worthiest novel's unacknowledged author (11)
I believe the answer is:
Here is my best explanation:
'unacknowledged author' is the definition.
'ghostwriter' can be an answer for 'author' (ghostwriter is a kind of author). I'm not certain of the 'unacknowledged' bit.
'king imprisons worthiest novel's' is the wordplay.
'king' becomes 'gr'.
'imprisons' is an insertion indicator.
'novel's' is an anagram indicator (I've seen 'novel' mean this).
'worthiest' anagrammed gives 'hostwrite'.
'gr' enclosing 'hostwrite' is 'GHOSTWRITER'.