Cracking crime coming first in mountain region (5)
I believe the answer is:
sinai
'mountain region' is the definition.
'Sinai' can be an answer for 'region' (Sinai is an example). I'm not certain of the 'mountain' bit.
'cracking crime coming first' is the wordplay.
'cracking' becomes 'AI' (resembles A1, informal term for excellent).
'crime' becomes 'sin'.
'coming first' says to put letters next to each other.
'ai' put after 'sin' is 'SINAI'.
'in' is the link.
Can you help me to learn more?
(Other definitions for sinai that I've seen before include "Mount where Moses received God's law" , "Deserted area" , "Mountainous peninsula in Egypt" , "11 Across peninsula" , "Mountainous Egyptian peninsula" .)