Emotionless soldier is close to defeat in heroic story (10)
I believe the answer is:
antiseptic
'emotionless' is the definition.
'soldier is close to defeat in heroic story' is the wordplay.
'soldier' becomes 'ant' (I've seen this before**).
'close to' suggests the final letters (the close/ending of).
'in' means one lot of letters goes inside another.
'heroic story' becomes 'epic' (I've seen this before).
The last letter of 'defeat' is 't'.
't' put within 'epic' is 'eptic'.
'ant'+'is'+'eptic'='ANTISEPTIC'
(Other definitions for antiseptic that I've seen before include "treatment" , "germicide" , "Preventing growth of, eg, bacteria" , "Designed to counteract infection" , "Preventing growth of microorganisms" .)