Lines going inside through country house (5)
I believe the answer is:
villa
'country house' is the definition.
(I know that villa is a type of country house)
'lines going inside through' is the wordplay.
'lines' becomes 'll' (two abbreviations for line).
'going inside' means one lot of letters goes inside another.
'through' becomes 'via' (via means going through).
'll' going into 'via' is 'VILLA'.
(Other definitions for villa that I've seen before include "where 6 [VERDI] lived?" , "Roman or suburban house" , "SECOND PART OF 8" , "Country residence" , "Aston ..., English Premier League club" .)