Essence of detective headquarters to contain trouble (12)
I believe the answer is:
distillation
'essence' is the definition.
(thesaurus)
'detective headquarters to contain trouble' is the wordplay.
'detective' becomes 'di' (Detective Inspector abbreviation).
'headquarters' becomes 'station' (I've seen this before).
'to contain' means one lot of letters goes inside another.
'trouble' becomes 'ill' ('ill' can be a synonym of 'trouble'**).
'station' placed around 'ill' is 'stillation'.
'di'+'stillation'='DISTILLATION'
'of' acts as a link.
(Other definitions for distillation that I've seen before include "Spirit-making process" , "Whisky-making process" , "Process for producing spirits" , "Process of making, eg, whisky" .)