Happening, brewing (5)
I believe the answer is:
afoot
This clue is a double definition.
'happening' is the first definition.
('something's afoot' means 'something's happening')
'brewing' is the second definition.
(I've seen this before)
(Other definitions for afoot that I've seen before include "in the air" , "Astir" , "Under way (like hunted game?)" , "In the pipeline" , "Progressing, in operation - like Sherlock Holmes's game" .)