Detective follows street maps of Mexican empire (5)
I believe the answer is:
aztec
'mexican empire' is the definition.
(I've seen this in another clue)
'detective follows street maps' is the wordplay.
'detective' becomes 'tec' (tec is short for detective).
'follows' is a charade indicator (letters next to each other).
'street maps' becomes 'az' (I am not sure about this - if you are sure you should believe this answer much more).
'tec' after 'az' is 'AZTEC'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for aztec that I've seen before include "Like Montezuma?" , "Native of old Mexico" , "Historical S. American" , "Such as Moctezuma" , "old American" .)