Impervious to nastiest crook stalking queen (9)
I believe the answer is:
resistant
'impervious to' is the definition.
(thesaurus)
'nastiest crook stalking queen' is the wordplay.
I cannot quite see how this works, but
an anagram of 'nastiest' is 'esistant' which is within the answer.
'queen' could be 'r' (abbreviation for regina, e.g. in ER ) and 'r' is found within the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for resistant that I've seen before include "unaffected" , "tough" , "not accommodating" , "Withstanding adverse conditions" , "Impervious to various sources of damage" .)