Deadly agent in The New Avengers (5,3)
I believe the answer is:
nerve gas
'deadly agent' is the definition.
'new avengers' is the wordplay.
'new' indicates anagramming the letters.
'avengers' with letters rearranged gives 'NERVE GAS'.
'in the' acts as a link.
(Other definitions for nerve gas that I've seen before include "Type of weapon" , "WW2 prison camp" , "Poisonous vapour" , "Chemical warfare agent" , "Dangerous concoction" .)