Crime of a king wanting male heir? (5)
I believe the answer is:
arson
'crime' is the definition.
(crime of illegally starting a fire)
'a king wanting male heir?' is the wordplay.
'king' becomes 'R' (abbreviation for rex, king in Latin).
'wanting' is a charade indicator (letters next to each other).
'male heir?' becomes 'son' (male child).
'a'+'r'+'son'='ARSON'
'of' is the link.
(Other definitions for arson that I've seen before include "Crime involving fire" , "Fire requiring forensic study" , "matchplay, say?" , "Criminal burning of property" , "Crime of fire-setting (5)" .)