Devious cronies concealing a plot (8)
I believe the answer is:
scenario
'plot' is the definition.
(I've seen this before)
'devious cronies concealing a' is the wordplay.
'devious' indicates anagramming the letters.
'concealing' indicates putting letters inside.
'cronies' is an anagram of 'scenrio'.
'scenrio' going around 'a' is 'SCENARIO'.
(Other definitions for scenario that I've seen before include "Written outline of a film, novel, or stage work" , "Story outline" , "Outlines of drama" , "Film/novel plot outline" , "Projected plan of action" .)