Starts to invade office, wandering around in a state (4)
I believe the answer is:
iowa
'a state' is the definition.
(I know that Iowa is a American state)
'starts to invade office wandering around' is the wordplay.
'starts to' says to take the initial letters.
The first letters of 'invade office wandering around' is 'IOWA'.
'in' is the link.
(Other definitions for iowa that I've seen before include "US state, capital Des Moines" , "part of US" , "Midwest US state" , "'Hawkeye State'" , "State of USA" .)