Alexander's troops taking what's inside (5)
I believe the answer is:
Here is my best explanation:
'alexander's' is the definition.
(sasha alexander is an actress)
'troops taking what's inside' is the subsidiary indication.
'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**).
(Other definitions for sasha that I've seen before include "Russian boy", "young man from Russia" and "Possible Russian".)