Announce resignation in city, after one evil act (8)
I believe the answer is:
iniquity
'evil act' is the definition.
(I've seen this before)
'announce resignation in city after one' is the wordplay.
'announce resignation' becomes 'iquit' ('I quit' is often used to announce a resignation).
'in' means one lot of letters goes inside another.
'city' becomes 'ny' (I've seen this in other clues**).
'after' means one lot of letters go next to another.
'one' becomes 'i' (Roman numeral).
'iquit' inserted inside 'ny' is 'niquity'.
'niquity' after 'i' is 'INIQUITY'.
(Other definitions for iniquity that I've seen before include "Lack of justice" , "Sin" , "Evil act" , "Gross injustice; crime" , "Great wickedness or injustice" .)