Happy for one taking part in Cold War film (5)
I believe the answer is:
dwarf
'happy for one' is the definition.
(I've seen this in another clue)
'part in cold war film' is the wordplay.
'part in' indicates a hidden word.
'DWARF' is hidden within 'cold war film'.
'taking' is the link.
(Other definitions for dwarf that I've seen before include "Doc or Happy, perhaps?" , "Grumpy, e.g." , "extra in Lord of the Rings?" , "Small mythological being" , "Small figure" .)