Help following Mark's servant (4)
I believe the answer is:
maid
'servant' is the definition.
(maid is a kind of servant)
'help following mark's' is the wordplay.
'help' becomes 'aid' ('aid' can be a synonym of 'help').
'following' is a charade indicator (letters next to each other).
'mark' becomes 'm'.
'aid' put after 'm' is 'MAID'.
(Other definitions for maid that I've seen before include "One in service" , "employee" , "Serving girl" , "Young woman - servant" , "daughter?" .)