Serious error getting second home (3)
I believe the answer is:
'serious error' is the definition.
(I've seen this before)
'second home' is the wordplay.
'second' becomes 's' (common abbreviation).
'home' becomes 'in' (to be in is to be (at) home).
'getting' is the link.
(Other definitions for sin that I've seen before include "Serious transgression" , "Immoral act" , "Moral offence" , "Pride, say" , "Evil" .)