Domestics help in case of magistrates (5)
I believe the answer is:
maids
'domestics' is the definition.
(maid is a kind of domestic)
'help in case of magistrates' is the wordplay.
'help' becomes 'aid' ('aid' can be a synonym of 'help'**).
'in' means one lot of letters goes inside another.
'case of' says to hollow out the word (remove centre letters) (outsides of).
'magistrates' with its centre taken out is 'ms'.
'aid' placed into 'ms' is 'MAIDS'.
(Other definitions for maids that I've seen before include "Lasses" , "girls!" , "Female domestic servants" , "Getting women in service" , "Female domestics" .)