Track down husband leaving ancient country (5)
I believe the answer is:
trace
'track down' is the definition.
(thesaurus)
'husband leaving ancient country' is the wordplay.
'husband' becomes 'h'.
'leaving' suggests deleting specific letters.
'ancient country' becomes 'thrace' (I've seen this before).
'thrace' with 'h' taken out is 'TRACE'.
(Other definitions for trace that I've seen before include "Evidence" , "Find; copy; small amount" , "Seek out" , "Find by investigation" , "plan" .)