Crafty old man meets a killer in the house (8)
I believe the answer is:
flypaper
'killer in the house' is the definition.
(material used to kill flies)
'crafty old man meets a' is the wordplay.
'crafty' becomes 'fly' (fly can mean shrewd or crafty).
'old man' becomes 'pa' (both can mean father).
'meets' is a charade indicator (letters next to each other).
'a' becomes 'per' (eg 'one a day' means 'one per day').
'fly'+'pa'+'per'='FLYPAPER'
(Other definitions for flypaper that I've seen before include "Sticky trap for bluebottles etc" , "one collecting insects" , "Sticky stuff to trap insects" , "pests will be caught by it" , "Sticky insect trap" .)