The foreigner driving the nail point in (5)
I believe the answer is:
alien
'the foreigner' is the definition.
('alien' can be a synonym of 'foreigner')
'driving the nail point in' is the wordplay.
'driving the nail' becomes 'an' (I can't justify this - if you can you should believe this answer much more).
'point' becomes 'lie' (lie is a kind of point).
'in' is an insertion indicator.
'an' placed around 'lie' is 'ALIEN'.
Can you help me to learn more?
(Other definitions for alien that I've seen before include "Creature from another planet" , "Unfamiliar; foreign" , "repugnant" , "One is from outer space, perhaps" , "extraneous" .)