Strange, finding fellow not at home, but that's the exception (3,3,3)
I believe the answer is:
odd man out
'that's the exception' is the definition.
I can't tell whether this defines the answer.
'strange finding fellow not at home' is the wordplay.
'strange' becomes 'odd' (I've seen this before).
'finding' means one lot of letters go next to another.
'fellow' becomes 'man' (fellow can mean a man).
'not at home' becomes 'out' (out can mean away from home).
'odd'+'man'+'out'='ODD MAN OUT'
'but' is the link.
Can you help me to learn more?
(Other definitions for odd man out that I've seen before include "film starring James Mason" , "that doesn't match the rest?" , "Method of selection" , "Atypical or unconventional person" , "Nonconformist" .)