Son breaks mirror in domed recess (4)
I believe the answer is:
apse
'domed recess' is the definition.
(I've seen this in another clue)
'son breaks mirror' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'breaks' means one lot of letters goes inside another.
'mirror' becomes 'ape' (I've seen this in another clue).
's' going into 'ape' is 'APSE'.
'in' is the link.
(Other definitions for apse that I've seen before include "Peas (anag) - found in church" , "Strange peas in the church recess" , "Church's part" , "Projection to the east end of a church" , "Church area" .)