Afghans regularly overthrown in epic story (4)
I believe the answer is:
saga
'epic story' is the definition.
(I've seen this in another clue)
'afghans regularly overthrown' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'overthrown' shows that the letters should be reversed in order.
The alternate letters of 'afghans' are 'agas'.
'agas' reversed gives 'SAGA'.
'in' is the link.
(Other definitions for saga that I've seen before include "Icelandic or Norse story" , "Tale of heroes" , "Epic tale" , "Long heroic, family, story" , "Norse epic" .)