One needs cracking finale in epic verse (4)
I believe the answer is:
code
'one needs cracking' is the definition.
(a code must be cracked)
'finale in epic verse' is the wordplay.
'finale in' indicates one should take the final letters (the final letter).
'verse' becomes 'ode' (ode is a type of poem or verse).
The final letter of 'epic' is 'c'.
'c'+'ode'='CODE'
(Other definitions for code that I've seen before include "Secret symbols" , "ethical principles?" , "Collection of laws" , "Method of encryption or set of rules" , "Computer language, say" .)