Magistrate contributing to bizarre evening (5)
I believe the answer is:
reeve
'magistrate' is the definition.
(I've seen this before)
'contributing to bizarre evening' is the wordplay.
'contributing to' indicates the answer is hidden within the clue.
'REEVE' is hidden within 'bizarre evening'.
(Other definitions for reeve that I've seen before include "Old judge" , "Chief magistrate (hist.); pass (rope) through hole" , "Could 'e ever pass a rope through a hole?" , "Former shire official" , "Female flyer" .)