Gold stolen by mischievous altar boy — might trial happen here? (10)
I believe the answer is:
laboratory
'might trial happen here?' is the definition.
'gold stolen by mischievous altar boy' is the wordplay.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'stolen by' means one lot of letters goes inside another.
'mischievous' indicates anagramming the letters.
'altar'+'boy'='altarboy'
'altarboy' with letters rearranged gives 'laboraty'.
'or' inserted inside 'laboraty' is 'LABORATORY'.
(Other definitions for laboratory that I've seen before include "Experimental area" , "workplace" , "Language-learning facility" , "Place of scientific research" , "Where litmus paper could be" .)