Get the member to finish an old story (6)
I believe the answer is:
legend
'an old story' is the definition.
(traditional story)
'get the member to finish' is the wordplay.
'get' means one lot of letters go next to another.
'the member' becomes 'leg' (member can mean a limb).
'to finish' becomes 'end' ('end' can be a synonym of 'finish').
'leg' put next to 'end' is 'LEGEND'.
(Other definitions for legend that I've seen before include "explanation" , "Saga" , "Person who has become famous" , "Story about mytical beings" , "extremely famous person?" .)