Line is written by this writer in second episode (10)
I believe the answer is:
instalment
'episode' is the definition.
('instalment' can be a synonym of 'episode')
'line is written by this writer in second' is the wordplay.
'line' becomes 'l'.
'is written by' means one lot of letters go next to another.
'this writer' becomes 'me' (the person who is writing these clues).
'in' means one lot of letters goes inside another.
'second' becomes 'instant' ('instant' can be a synonym of 'second'**).
'l'+'me'='lme'
'lme' placed inside 'instant' is 'INSTALMENT'.
(Other definitions for instalment that I've seen before include "One of a series of partial payments" , "episode" , "Payment of part of debt" , "part of serial" , "Chapter" .)