A new terrorist leader in charge of caper (5)
I believe the answer is:
antic
'caper' is the definition.
('antic' can be a synonym of 'caper')
'a new terrorist leader in charge' is the wordplay.
'a new' becomes 'an' (I've seen this in other clues).
'leader' suggests taking the first letters.
'in charge' becomes 'ic'.
The first letter of 'terrorist' is 't'.
'an'+'t'+'ic'='ANTIC'
'of' acts as a link.
(Other definitions for antic that I've seen before include "Tomfoolery" , "Caper, trick" , "Prank" , "Playful caper" , "Grotesque, fantastic (archaic)" .)