Announce the lady's mistreated lad (6)
I believe the answer is:
herald
'announce' is the definition.
('herald' can be a synonym of 'announce')
'the lady's mistreated lad' is the wordplay.
'the lady' becomes 'her' (I've seen this before**).
'mistreated' is an anagram indicator.
'lad' is an anagram of 'ald'.
'her'+'ald'='HERALD'
(Other definitions for herald that I've seen before include "Bringer of news" , "and 14: 'Hark! The -- -- sing' (carol)" , "Person who announces important news" , "Usher in; proclaim" , "Foreshadow" .)