One delayed more surprisingly by US city investigator (9)
I believe the answer is:
latecomer
'one delayed' is the definition.
I can't judge whether this defines the answer.
'more surprisingly by us city investigator' is the wordplay.
'surprisingly' is an anagram indicator.
'by' is a charade indicator (letters next to each other).
'us city' becomes 'la'.
'investigator' becomes 'tec' (short for 'detective').
'more' with letters rearranged gives 'omer'.
'la'+'tec'='latec'
'omer' put after 'latec' is 'LATECOMER'.
Can you help me to learn more?
(Other definitions for latecomer that I've seen before include "Person arriving behind time" , "Recent convert" , "Recent or tardy arrival" , "one's a poor timekeeper" , "Perhaps one held up" .)