Work at home? It's murder! (2,2)
I believe the answer is:
do in
'murder' is the definition.
(thesaurus)
'work at home?' is the wordplay.
'work' becomes 'do' ('do work' can be a synonym of 'work'**).
'at home?' becomes 'in' ('in' can be similar in meaning to 'at home').
'do'+'in'='DO IN'
'it's' acts as a link.
(Other definitions for do in that I've seen before include "Murder" , "Knock off" , "Get rid of" .)