Intriguing group from California set up research establishment (5)
I believe the answer is:
cabal
'intriguing group' is the definition.
(I've seen this in another clue)
'california set up research establishment' is the wordplay.
'california' becomes 'ca' (abbreviation).
'set up' shows that the letters should be reversed in order (in a down clue, letters go up).
'research establishment' becomes 'lab' (laboratory).
'lab' in reverse letter order is 'bal'.
'ca'+'bal'='CABAL'
'from' acts as a link.
(Other definitions for cabal that I've seen before include "Group of conspirators" , "Intriguing group" , "Plotting group" , "Intrigue, clique" , "Secret plot or the people engaged in it" .)