Plan to have church following Saint Mark? (7)
I believe the answer is:
splotch
'mark?' is the definition.
(thesaurus)
'plan to have church following saint' is the wordplay.
'plan' becomes 'plot' (plotting is a kind of planning**).
'to have' means one lot of letters go next to another.
'church' becomes 'ch' (common abbreviation).
'following' is a charade indicator (letters next to each other).
'saint' becomes 's'.
'plot' next to 'ch' is 'plotch'.
'plotch' put after 's' is 'SPLOTCH'.
(Other definitions for splotch that I've seen before include "Mark" , "Spot, splash, smear" .)