One of us at home is turning ruddy contrary (7)
I believe the answer is:
insider
'one of us' is the definition.
(thesaurus)
'home is turning ruddy contrary' is the wordplay.
'home' becomes 'in' ('he's home' can mean 'he's in').
'turning' says the letters should be written in reverse.
'ruddy' becomes 'red' ('red' can be a synonym of 'ruddy').
'contrary' says the letters should be written in reverse.
'is' backwards is 'si'.
'red' written backwards gives 'der'.
'in'+'si'+'der'='INSIDER'
'at' acts as a link.
(Other definitions for insider that I've seen before include "One with privileged info" , "member of favoured group?" , "One dealing illegally" , "person with the lowdown" , "Member of select group in the know" .)