Son accompanying old man in health resort (3)
I believe the answer is:
spa
'health resort' is the definition.
(spa can mean a health resort)
'son accompanying old man' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'accompanying' is a charade indicator (letters next to each other).
'old man' becomes 'pa' (both can mean someone's father).
's'+'pa'='SPA'
'in' is the link.
(Other definitions for spa that I've seen before include "town for his health!" , "Health and beauty treatment establishment" , "here for healthy holiday" , "health centre" , "Bath - mineral water spring" .)