The affair of the bag (4)
I believe the answer is:
case
This clue is a double definition.
'the affair' is the first definition.
'the bag' is the second definition.
(I have seen 'Overnight bag' mean 'case' so perhaps 'bag' could also mean 'case')
'of' acts as a link.
(Other definitions for case that I've seen before include "Reconnoitre" , "Instance - container" , "Police investigation" , "Trunk" , "Judge tries this" .)