Alexander's troops taking what's inside (5)
I believe the answer is:
sasha
'alexander's' is the definition.
(sasha alexander is an actress)
'troops taking what's inside' is the wordplay.
'troops' becomes 'sas' (special air service).
'taking' means one lot of letters go next to another.
'what's inside' becomes 'ha' (ha is inside what**).
'sas'+'ha'='SASHA'
(Other definitions for sasha that I've seen before include "Russian boy" , "Possible Russian" , "young man from Russia" .)