Non-national enemy seizes power with queen (9)
I believe the answer is:
foreigner
'non-national' is the definition.
(someone from another nation)
'enemy seizes power with queen' is the wordplay.
'enemy' becomes 'foe' (synonyms).
'seizes' means one lot of letters goes inside another.
'power' becomes 'reign' (reign can mean time in power).
'with' is a charade indicator (letters next to each other).
'queen' becomes 'r' (r is abbreviation regina. e.g. in ER ).
'foe' going around 'reign' is 'foreigne'.
'foreigne'+'r'='FOREIGNER'
(Other definitions for foreigner that I've seen before include "Alien" , "asylum seeker?" , "chauvinist holds in contempt" , "One from abroad" , "Stranger, outsider" .)