Ogre in old church (3)
I believe the answer is:
orc
'ogre' is the definition.
(I've seen this in another clue)
'old church' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'church' becomes 'rc' (abbreviation for Roman Catholic).
'o'+'rc'='ORC'
'in' acts as a link.
(Other definitions for orc that I've seen before include "Tolkienian creature" , "Imaginary creature" , "Tolkienian monster" , "warlike figure" , "Tolkien's creation" .)