Covert criminal trio pursues it (13)
I believe the answer is:
surreptitious
'covert' is the definition.
('surreptitious' can be similar in meaning to 'covert')
'criminal trio pursues it' is the wordplay.
'criminal' indicates an anagram.
'trio'+'pursues'+'it'='triopursuesit'
'triopursuesit' with letters rearranged gives 'SURREPTITIOUS'.
(Other definitions for surreptitious that I've seen before include "Sly" , "Done in secret; stealthy" , "Done covertly" , "Done by stealth" , "Covert, clandestine" .)