One involved in the shop's accounts (7)
I believe the answer is:
stories
'accounts' is the definition.
(I know this)
'one involved in the shop's' is the wordplay.
'one' becomes 'i' (Roman numeral).
'involved in' means one lot of letters goes inside another.
'the shop's' becomes 'stores' ('store' can be a synonym of 'shop').
'i' inserted into 'stores' is 'STORIES'.
(Other definitions for stories that I've seen before include "For example, scoops" , "Tales" , "See 12" , "Lies" , "House sections" .)