Detectives going back on record is nothing irregular (8)
I believe the answer is:
Here is my best explanation:
'irregular' is the definition.
'detectives going back on record is nothing' is the subsidiary indication.
'detectives' becomes 'cid'.
'going back' shows that the letters should be reversed in order.
'on' says to put letters next to each other.
'record' becomes 'ep'.
'nothing' becomes 'o' (looks like zero - 0).
'cid' backwards is 'dic'.
'dic' after 'episo' is 'episodic'.
(Other definitions for episodic that I've seen before include "Occurring irregularly - is copied thus", "Presented in sections", "In parts", "Discursive", "in serial form", "Occurring irregularly or in instalments", "taken one piece at a time", "Having a sporadic", "Irregular" and "piecemeal".)