Mislay record before show (8)
I believe the answer is:
disclose
'show' is the definition.
(I've seen this before)
'mislay record before' is the wordplay.
'mislay' becomes 'lose' (synonyms).
'record' becomes 'disc' (eg a CD, compact disc).
'before' means one lot of letters go next to another.
'lose' put after 'disc' is 'DISCLOSE'.
(Other definitions for disclose that I've seen before include "Make public" , "Sold ices (anag)" , "Report" , "show" , "Lay bare" .)