It's murder prior to midnight performance (5)
I believe the answer is:
doing
'performance' is the definition.
('doing' can be a synonym of 'performance')
'it's murder prior to midnight' is the wordplay.
'it's murder' becomes 'doin' (I've seen this before).
'prior to' says to put letters next to each other.
'midnight' becomes 'g'.
'doin'+'g'='DOING'
(Other definitions for doing that I've seen before include "Carrying out action" , "deed?" , "Hoaxing" , "Faring" , "Performing a task" .)